In most ways, mech combat follows the same rules as tactical combat: mechs
take multiple actions each round to move, attack, and activate abilities. See
Chapter 8 of the Starfinder Core Rulebook for tactical combat rules.
The biggest differences in mech combat are size and action economy. Mechs are immense, and they are able to control large spaces, travel quickly, and even affect areas with their attacks. Mech control systems also allow multiple operators to act in concert, enabling many mechs to perform a host of actions on their turns.
Mechs are designed to function seamlessly on the same battle maps made up of 5-foot-by-5-foot squares commonly used for Starfinder tactical combat. However, for mech encounters over larger areas or against larger foes, it also works well to treat each square as a 10-foot-by-10-foot area. Most mech size and distance values are divisible by 10; in rare cases where a range or size value is divisible by 5 but not by 10, round the value down to the nearest value divisible by 10. Thus, a Huge mech that would occupy a 15-foot-by15-foot space would occupy a single square using a 10-foot scale, and a Huge mech’s reach would be 10 feet (one square) rather than 15 feet.
Each mech can accommodate one or more operators who share control over the
mech’s movement, armaments, and other systems. Operators share a pool of actions
and work together to control their machine (see Mech Actions below). Each mech
requires a minimum number of operators to function and has a maximum number
of operators it can accommodate.
A character can board an allied or unattended mech in an adjacent space as a full action, becoming one of that mech’s operators. An operator can disembark a mech as a full action, emerging in any empty space adjacent to the mech. At the GM’s discretion, an unattended mech can require an operator to succeed at a Computers check to hack it in order to initially gain control of that mech (DC = 20 + 1-1/2 the mech’s tier).
A mech blocks line of effect to and from its operators. If a mech is destroyed (see Taking Damage on page 14), additional damage dealt to the mech is instead dealt to a random operator inside; that operator can attempt a DC 20 Reflex save to take half damage.
A mech’s available actions per turn depend on the number of operators currently
controlling it. While at least one operator is controlling it, a mech can take
one move action per turn and one reaction per round.
Operators can take a full action to pilot a mech, granting it an additional move action or standard action that turn (maximum six additional actions per turn). A mech can perform a full action either in place of a standard and move action or in place of two standard actions. Regardless of its total number of actions, a mech can’t use more than two actions to move each turn, and it can’t activate any one mech component (such as a weapon or auxiliary system; see pages 20–24) more than once per round unless otherwise noted.
For example, if a mech has four operators and each takes a full action to grant the mech actions, the mech can take up to four standard actions and one move action. The mech could use these actions to move its speed and attack once each with four different weapons. Alternatively, the mech could move its speed twice, attack once with one weapon, and make a full attack with another weapon. There are many other options available, depending on the mech’s available systems.
Skills: A mech with at least one operator can take the appropriate action, if any, to attempt Acrobatics, Athletics, and Perception skill checks, as well as Intimidate checks to demoralize. Some frames and auxiliary systems allow mechs to use additional skills. See below for calculating a mech’s skill modifiers.
Guarded Step: When using the guarded step action, a mech can move up to 10 feet without provoking an attack of opportunity
A mech’s actions represent a combination of its operators’ skill and its
own sophisticated machinery, and the modifiers a mech uses when performing actions
reflects this union. When an operator grants a mech an action, the mech uses
that operator’s relevant bonus or skill ranks to help calculate the mech’s total
modifier. If more than one operator contributes to the same action—such as two
operators working together to grant their mech a full action—the mech uses the
higher of the two operators’ statistics when calculating its modifier.
Common modifiers and text describing how to calculate them can be found below.
Mech Attacks: A mech’s attack roll is calculated using the following formula. A mech’s melee attack modifier and ranged attack modifier can differ depending on the components used to build the mech.
|Mech Attack = 1d20 + 8 + 1/5 the mech’s tier + bonuses from upper limb components (upper limb weapons only) + the operator’s base attack bonus or the operator’s ranks in the Piloting skill + bonuses from the weapon + range penalty|
Strength Modifier: A mech doesn’t have ability scores. It
does, however, have an effective Strength score used for calculating its melee
damage modifiers and resolving Strength checks to break objects. A mech’s Strength
modifier is based on its frame and upperlimb component. In addition, a mech’s
Strength modifier increases by 1 at tier 4 and by an additional 1 for every
3 tiers thereafter.
Damage Modifiers: A mech adds its tier to all weapon damage rolls. A mech adds its Strength modifier to its melee damage rolls.
Armor Class: A mech’s EAC and KAC are each calculated using the same formula, though the modifiers applied may differ depending on the mech’s components.
|Armor Class = 13 + (1-1/4 the mech’s tier) + bonus from frame + bonus from upper limbs + bonus from lower limbs|
Initiative Modifier: A mech’s initiative modifier equals
the lowest initiative modifier among its operators (minimum +0). A mech’s minimum
initiative modifier increases by 1 at tier 5 and every 5 levels thereafter.
Saving Throw Modifiers: A mech’s base saving throw modifiers equal 2 + 3/4 the mech’s tier. Various mech components such as its frame, lower limbs, and upper limbs can increase these modifiers.
Skill Modifiers: A mech’s skill check modifier equals 5 + half its tier; for Athletics checks, also add the mech’s Strength modifier. When an operator grants their mech an action and the mech performs a skill check as part of that action, the mech can use the operator’s ranks in that skill in place of half the mech’s tier to determine its modifier. When performing a Strength- or Dexterity-based skill check, a mech can instead use its operator’s ranks in Piloting to determine the mech’s skill modifier.
Each mech’s power core provides it ample energy to move and fight while also
generating excess power—measured in Power Points (PP)— that the mech can exploit
to supercharge its systems. A mech’s power core determines how many PP it begins
each encounter with, how many it can store at a time, and how many it generates
at the end of each turn. Many auxiliary systems, weapons, and other components
have special abilities that require expending PP to function.
In addition, there are several Power Point abilities available to all mechs that can be used without spending actions. None of these abilities can be applied to the same check more than once.
Aim (1 PP): Before attempting an attack roll, the mech can activate this ability to roll 1d4 and add the result as an insight bonus to the attack roll.
Devastating Hit (3 PP): After hitting a creature with an attack, but before dealing damage, the mech increases its weapon’s damage value by one step against that creature (e.g. medium damage instead deals high damage). A weapon that already deals extreme damage instead adds 1 additional damage for every damage die rolled for the attack. This ability can’t be used for weapons that attack an intersection rather than a creature, such as weapons with the explode weapon special property.
Maneuver (1 PP): Choose one skill. Until the beginning of the mech’s next turn, operators add any insight bonus they have that applies to that skill to the mech’s checks with that skill.
Replenish (2 PP): Activate this ability when regaining Shield Points. The number of SP the mech recovers increases by 1d8. This increases by an additional 1d8 at tier 5 and every 5 tiers thereafter.
Resist (1 PP): Before attempting a saving throw the mech can activate this ability to roll 1d4 and add the result as a resistance bonus to the saving throw.
In addition to the actions detailed in Chapter 8 of the Core Rulebook, mechs
can perform the following special actions.
Called Shot (Standard Action): The mech expends either 1 PP or 3 PP and makes an attack against a single mech. If the attack’s damage causes system damage, the operator can choose which component takes system damage, except the power core or helm; if the mech expended 3 PP, the operator can select any component to take the system damage.
Hurl (Full Action): The mech grabs a nearby object and throws it as a ranged attack with a range increment of 30 feet. The object can be at largest two size categories smaller than the mech. For an object of the maximum size or next smallest size, the attack deals medium damage to the thrown object and the target as if it were a weapon whose level equals the mech’s tier. For any smaller object, the weapon deals light damage instead.
The mech can use this ability to grab and throw a creature or moving vehicle within reach, but to do so the mech must also succeed at a grapple combat maneuver against the creature to be thrown. If the combat maneuver fails, the hurl action fails, but the mech gains a move action (effectively wasting a standard action).
Scan (Move Action): The mech uses its sensor array to study one creature or object it is observing with a precise sense. Against a creature, this functions as a check to identify a creature, using the mech’s Computers bonus in place of the skill typically used to identify creatures of that type. If the check succeeds, the mech also gains a +1 insight bonus to the next attack it makes against that creature before the end of its next turn.
If the mech scans an object (including a vehicle or mech), the mech attempts a Computers check; against an unattended object, the DC is 10, and against a wielded or piloted object, the DC equals 10 plus the target’s tier or item level. If it succeeds, the mech identifies two of the following pieces of information about the object (operator’s choice): its hardness, its maximum Hit Points, its resistances (if any), its EAC, its KAC, its number of passengers or operators, its Strength DC to break, its speed, its full speed (vehicle only), its systems or auxiliary systems, or its weapons. For every 5 by which the Computers check exceeds the DC, the mech identifies one additional piece of information.
Repeated scans reveal little information unless the mech expends additional energy. Each additional attempt to scan a target requires the mech expend 1 PP for each previous time the mech’s attempted to scan that target within the last hour.
Mechs typically have a combination of Hit Points (HP) and Shield Points (SP)
that collectively represent how much damage a mech can sustain before taking
penalties or ceasing to function altogether. When a mech takes damage, the damage
is first applied to its Shield Points. If its SP are reduced to 0, its shields
become inactive until the beginning of the mech’s next turn; for any excess
damage, reduce the damage by the mech’s hardness (if any), and apply all remaining
damage to the mech’s Hit Points.
At the start of its turn, a mech regains a number of Shield Points equal to its tier, though its total can’t exceed the mech’s maximum Shield Points.
If a mech is reduced to 0 Hit Points, it is wrecked. A wrecked mech can’t perform actions, including sustaining its altitude or depth if airborne or underwater; such mechs typically fall or sink, taking damage as normal. A wrecked mech’s operators aren’t necessarily in danger, though a mech wrecked in a precarious location could be perilous. A wrecked mech can be repaired (see Repairing Damage below).
If a mech ever takes damage that exceeds twice its Hit Points, it is destroyed and can’t be repaired.
As a mech takes damage, its various components can malfunction or become
outright inoperable. Whenever a mech takes enough damage to be reduced to two-thirds
its remaining Hit Points, and again when it takes enough damage to be reduced
to one-third its remaining Hit Points, it experiences system failure. To determine
which component is affected, roll 1d20 and consult the table below.
If the component doesn’t currently have a system failure, it gains the malfunctioning condition. If the component already has the malfunctioning condition, it gains the inoperable condition. These conditions are explained below.
Overcoming System Failure: Although system damage is devastating, a mech can temporarily overcome these setbacks. At the beginning of its turn, a mech can either spend 2 PP to ignore the malfunctioning condition for any one component or spend 4 PP to treat one component’s inoperable condition as malfunctioning.
Upper Limb: A mech with malfunctioning upper limbs takes
a –2 penalty to attack rolls with weapons mounted in upper-limb slots, as well
as to any combat maneuvers that don’t use a mech weapon. A mech with inoperable
upper limbs can’t use weapons mounted in upper-limb slots.
Lower Limb: A mech with malfunctioning lower limbs halves movement speeds not provided by an auxiliary system, and the mech takes a –2 penalty to attack rolls with weapons mounted in lower limb slots. If the lower limbs become inoperable, these speeds are reduced to 0; if the mech is hovering or flying using any of these speeds, it begins falling. A mech with inoperable lower limbs can’t use weapons mounted in its lower-limb slots.
Frame: A mech with a malfunctioning frame takes a –2 penalty to attack rolls with weapons mounted in frame slots, and the mech halves its hardness, if any. A mech with an inoperable frame can’t use weapons mounted in frame slots, and the mech’s hardness is reduced to 0.
Auxiliary System: Whenever a mech with malfunctioning auxiliary systems attempts to activate an auxiliary system, there is a 25% chance that the auxiliary system does not function and can’t be used until the beginning of the mech’s next turn; any action and PP used to activate the auxiliary system are wasted. Any auxiliary systems that provide a constant benefit have a 25% chance of not functioning for 1 round at the beginning of each turn.
Auxiliary systems with the inoperable condition behave as though they had the malfunctioning condition, with two exceptions. First, the chance of failure increases to 50%. Second, upon gaining the inoperable condition, select one auxiliary system at random; that auxiliary system ceases to function.
Power Core: The rate at which a mech with a malfunctioning power core regains lost Shield Points and Power Points is halved. The rate at which a mech with an inoperable power core regains lost Shield Points and Power Points is reduced to 0. When a mech’s power core first gains the malfunctioning condition and again when it gains the inoperable condition, the mech loses 1d4 PP.
Helm: The helm represents the cockpit or control center where the operators reside, and the helm’s system failure doesn’t directly impede the mech but instead threatens one or more operators. When the helm gains the malfunctioning condition, half of the operators (rounded up) take bludgeoning damage equal to 1d8 damage times the mech’s tier; they can attempt a Reflex saving throw to halve the damage (DC = 15 + half the mech’s tier). When the helm gains the inoperable condition, each of the operators takes the bludgeoning damage above (Reflex half). In addition, the operators’ controls become unreliable; the first time each turn that an operator uses a full action to pilot the mech, there is a 50% chance that the mech does not gain an action.
Either effect lasts until the beginning of the mech’s next turn.
When a mech combat encounter is over, its operators can repair damage dealt
to their mech, provided it hasn’t been destroyed or lost. Performing repairs
requires stopping the mech, disembarking, and working on the mech’s exterior.
Any number of allies can use the aid another action to assist with the Engineering
checks involved in repairing a mech.
You can remove system failure conditions from a component by spending 10 minutes working on the mech and succeeding at an Engineering check. The DC depends on the severity of the condition: DC 20 for malfunctioning and DC 25 for inoperable. If you succeed, you remove that component’s system failure condition, and the component can function as normal.
Restoring lost Hit Points is fairly difficult and resource intensive. You can restore a number of Hit Points equal to twice the mech’s tier by spending 1 hour performing repairs, succeeding at an Engineering check (DC = 10 + 1-1/2 times the mech’s tier), and expending 10 UPBs per point of damage to be repaired. If you exceed the check’s DC by 5 or more, you can reduce the repair time by half or the UPB cost by half. If you exceed the check’s DC by 10 or more, you instead reduce the time and cost by half. If you fail the check by 4 or less, you choose either to make no progress or to increase the UPB cost per Hit Point by 5 for that hour’s repairs. If you fail by 5 or more, you make no progress.
Shield Points regenerate out of combat automatically at a rate of 2 per hour.