GM Core
Chapter 1: Running the Game
Running Encounters
Running the Encounter
Special Battles and Movement
Vehicular and Mounted Combat
Source GM Core pg. 29
Vehicles are everywhere in Starfinder, from sleek enercycles to bulky hovercabs, and while mounted travel is considered by some to be an antiquated mode of travel, mounted combat is far from a lost art.
The logistics of vehicular combat and mounted combat take some extra work. Ensure the fight takes place in a location with plenty of space to move since you'll likely be dealing with multiple larger creatures or vehicles. For a fight in which only one side has vehicles or mounts, you might want to use an environment with a few areas too small for vehicles and mounts, so the side on foot can get a tactical advantage there to offset the other side's greater mobility.
When the PCs are mounted, their enemies should focus most of their attacks on the PCs, not their mounts. When PCs fight mounted enemies, try to keep the mount's level fairly close to the PCs' level; rather than putting an 11th-level enemy on a 2nd-level shotalashu, use a 9th-level surnoch, an 8th-level arabuk, or something similar. This will fit better thematically and prevent the enemy from being dismounted too easily. If a mount is knocked out, the rider might be able to dismount without trouble if the mount was stationary, but if they were in motion, you should probably have the rider attempt a Reflex save. If they fail, the rider is thrown a short distance and falls prone. Setting a simple expert DC of 20 often works well for such checks.
When the PCs are driving vehicles, their enemies should focus most of their attacks on the PCs, not their vehicles. Alternatively, if the PCs have greater or total cover while within their vehicle, their enemies should focus on either forcing or drawing the PCs out of their vehicle or on boarding the vehicle. When the PCs fight enemies in vehicles, try to keep the vehicle's level fairly close to the PCs' level. Consider the transport method of selected vehicles. Enemies driving wheeled vehicles are easier to stop or hinder than enemies driving hover vehicles, and the tactics PCs can employ against such enemies should likewise differ.
Vehicular and mounted combat on a grid is difficult for a running fight with both sides racing at full speed. In these situations, it's better to forgo the grid, though miniatures can still help for relative positioning and distances for ranged attacks. For such a race, consider using the chase subsystem instead.
The mount rules are for common cases: intelligent creatures riding animals. However, you might allow someone to ride a beast, robot, or other type of creature by making a few adjustments. For an intelligent mount (such as a skreesire), use the standard rules for mounted combat, but instead of attempting a check to Command an Animal, the rider uses the same number of actions to ask the creature to do what they want. As the GM, you determine whether the creature does as requested and whether Diplomacy checks or the like are needed. For a technological mount, instead replace the check to Command an Animal with a Computers check. If one of your PCs is Tiny, they might want to ride on another PC's shoulder. In this case, the two PCs should both roll initiative and act together on the lower count, and they gain only two actions at the start of their turns instead of three since the larger PC must spend one action keeping the smaller PC balanced, and the smaller PC must spend one action holding on.
The logistics of vehicular combat and mounted combat take some extra work. Ensure the fight takes place in a location with plenty of space to move since you'll likely be dealing with multiple larger creatures or vehicles. For a fight in which only one side has vehicles or mounts, you might want to use an environment with a few areas too small for vehicles and mounts, so the side on foot can get a tactical advantage there to offset the other side's greater mobility.
When the PCs are mounted, their enemies should focus most of their attacks on the PCs, not their mounts. When PCs fight mounted enemies, try to keep the mount's level fairly close to the PCs' level; rather than putting an 11th-level enemy on a 2nd-level shotalashu, use a 9th-level surnoch, an 8th-level arabuk, or something similar. This will fit better thematically and prevent the enemy from being dismounted too easily. If a mount is knocked out, the rider might be able to dismount without trouble if the mount was stationary, but if they were in motion, you should probably have the rider attempt a Reflex save. If they fail, the rider is thrown a short distance and falls prone. Setting a simple expert DC of 20 often works well for such checks.
When the PCs are driving vehicles, their enemies should focus most of their attacks on the PCs, not their vehicles. Alternatively, if the PCs have greater or total cover while within their vehicle, their enemies should focus on either forcing or drawing the PCs out of their vehicle or on boarding the vehicle. When the PCs fight enemies in vehicles, try to keep the vehicle's level fairly close to the PCs' level. Consider the transport method of selected vehicles. Enemies driving wheeled vehicles are easier to stop or hinder than enemies driving hover vehicles, and the tactics PCs can employ against such enemies should likewise differ.
Vehicular and mounted combat on a grid is difficult for a running fight with both sides racing at full speed. In these situations, it's better to forgo the grid, though miniatures can still help for relative positioning and distances for ranged attacks. For such a race, consider using the chase subsystem instead.
The mount rules are for common cases: intelligent creatures riding animals. However, you might allow someone to ride a beast, robot, or other type of creature by making a few adjustments. For an intelligent mount (such as a skreesire), use the standard rules for mounted combat, but instead of attempting a check to Command an Animal, the rider uses the same number of actions to ask the creature to do what they want. As the GM, you determine whether the creature does as requested and whether Diplomacy checks or the like are needed. For a technological mount, instead replace the check to Command an Animal with a Computers check. If one of your PCs is Tiny, they might want to ride on another PC's shoulder. In this case, the two PCs should both roll initiative and act together on the lower count, and they gain only two actions at the start of their turns instead of three since the larger PC must spend one action keeping the smaller PC balanced, and the smaller PC must spend one action holding on.