Two Combat Systems, One Game

[GMMichael]

I guess this is not what you're looking for, but for me D&D itself offers at least two combat systems: TotM and the full default combat system . . .
I know many DMs who use TotM for short, unimportant battles and the full system for featured encounters. Personally I even occasionally skipped the combat rules completely and reduce trivial encounters to a couple of rolls, making something up in terms of random possible costs for the PCs. Even if you just decide not to use HP for smaller monsters and let them die at the first hit, in a sense you're using an alternative combat system.

D&D does seem to allow an alternative way to fight if you use the non-combat rules, but it's pretty hard to see given how the combat rules are woven throughout everything else.

D&D might be a good example though. It seems you're referring to the DM(s) making the decisions on which system to use. How do the PCs feel about the choice of system? Or more specifically - how do the PCs feel, given the type of characters that they are playing? Are the non-warriors glad to see a TotM battle? Do the warrior-types feel that they're missing out if not all combat rules are used?

Would you let the PCs choose the system at the start of combat?

 

[Li Shenron]

D&D does seem to allow an alternative way to fight if you use the non-combat rules, but it's pretty hard to see given how the combat rules are woven throughout everything else.

D&D might be a good example though. It seems you're referring to the DM(s) making the decisions on which system to use. How do the PCs feel about the choice of system? Or more specifically - how do the PCs feel, given the type of characters that they are playing? Are the non-warriors glad to see a TotM battle? Do the warrior-types feel that they're missing out if not all combat rules are used?

Would you let the PCs choose the system at the start of combat?

When I used a simplified combat resolution instead of full combat rules, it was because the combat was easy and the details not important (the important part was the players' own choice to deal with the situation by force rather than in other ways). It would have been a waste of time to run the combat with the full rules, so I think even the most tactical of players were happy to move on, they probably would have considered it a pushover and not a real combat.

When I used TotM (mostly full combat rules except for handwaving exact ranges, directions, areas) the reason was typically that the environment didn't offer much to work with for instance in terms of cover, higher ground, and interactive scenery.

 

[Fifinjir]

Haven’t played them, but Runequest and Mythras have a separate combat system for exorcising spirits.