This is something that features in many strategy games to (usually) good effect.
This can really mean anything from the x2 versus units with a movement of 2 unit flag in Civ2 (that never really worked
) to separate stats for each unit versus each other unit type.
The other type of modifier is that of terrain:
Terrain in Civ3 and Civ2 already use a simple system of giving defence bonuses to units on those squares. Players have expressed interest in terrain that gives different bonuses for different unit types. Civ3 has a feature that allows the selected unit to ignore movement cost (above 1 MP) on selected terrain. That is a good example of a movement modifier. The idea is to elaborate on that and extend it to combat.
Ideally, the two types pf modifier would compensate each other (i.e. x unit has x stats vs. x unit while on x terrain).
The advantages of adding modifiers are clear: certain units have clear advantages under certain conditions. The cons are that new modders might be overwhelmed by too complex a system and that it *could* require a slightly more complex combat system in order to prevent exploits.
Some commentary on the subject from another thread on the same subject only applied to Civ3:
http://forums.civfanatics.com/showthread.php?s=&threadid=65557
Please comment and post your ideas.
This can really mean anything from the x2 versus units with a movement of 2 unit flag in Civ2 (that never really worked

The other type of modifier is that of terrain:
Terrain in Civ3 and Civ2 already use a simple system of giving defence bonuses to units on those squares. Players have expressed interest in terrain that gives different bonuses for different unit types. Civ3 has a feature that allows the selected unit to ignore movement cost (above 1 MP) on selected terrain. That is a good example of a movement modifier. The idea is to elaborate on that and extend it to combat.
Ideally, the two types pf modifier would compensate each other (i.e. x unit has x stats vs. x unit while on x terrain).
The advantages of adding modifiers are clear: certain units have clear advantages under certain conditions. The cons are that new modders might be overwhelmed by too complex a system and that it *could* require a slightly more complex combat system in order to prevent exploits.
Some commentary on the subject from another thread on the same subject only applied to Civ3:
http://forums.civfanatics.com/showthread.php?s=&threadid=65557
Please comment and post your ideas.