D&D 5E XCOM-like rules for a modern or sci-fi version of the 5e rules?

[Kobold Avenger]

With the common trend of nearly all turn-based video games with tactical combat to have cover (half and full) and overwatch as an action that seems to have started in XCOM: Enemy Unknown. I'm wondering if these things brought over to a system with a 5e base require new rules/changes or just the existing 5e rules on cover and readied actions?

 

[Sorcerers Apprentice]

The existing rules are fine for this style of play.

 

[Bayushi_seikuro]

I'd agree that the basics are already in the system, depending on how robust you need or want it to be. Just instead of bonus actions, action reaction, maybe use Move, Attack, Overwatch - maybe you can do Move + any of the three in one round: Move/Move, Move/Attack, Move/Overwatch. I'd watch out for having anything that would let someone Attack/Attack or Attack/Overwatch since the 5e stuff has its own action economy. YMMV.
My other question would be why are you wanting to use a 5e base in particular? There are modern d20 games out there, or other non-5e games. Some of them might be worth a look.

 

[MarkB]

You could go with the existing rules, or you could overhaul things to make cover a more fundamental aspect of the combat system. In XCOM being out of cover is basically death - you expect to be hit, and hit hard.

You could go with no cover meaning attacks against you automatically have advantage, normal cover means attacks are made normally, and high cover means attacks against you have disadvantage. You'd want to go with ranged attacks being the default for most classes, with only few area-effect or melee options, to keep the emphasis upon cover and position.

 

[Minigiant]

If you want X-COM gameplay, you attach a 1d10 roll to every attack roll.

If you roll a 1 on that d10, you miss regardless of what the d20 roll was.

"99% chance to hit my butt"

 

[RobJN]

Doesn't using the "Ready" action pretty much accomplish what Overwatch does..?

 

[Gammadoodler]

If you want X-COM gameplay, you attach a 1d10 roll to every attack roll.

If you roll a 1 on that d10, you miss regardless of what the d20 roll was.

"99% chance to hit my butt"

The number of times I've yelled at my TV after my captain ranked shotgun bro misses the little alien bastard with one pip of health left at point blank range....

 

[Warforged DK]

I've thought about that Overwatch type rule for a Mass Effect 5e game I intend to run in 2021. I figure it's honestly just the Ready Action. Maybe a feat that lets you Overwatch as a bonus action after Attack, or rework Sentinel to be like Overwatch, but only a small area, 3x3 maybe.
Also- @MarkB the idea of out of Cover=Advantage, half cover is normal and full cover is Disadvantage is damned genius for an XCOM style game. I don't think it'll work for my Mass Effect 5e game though, too many Vanguards charging in and wrecking sh*t and never in cover.

 

[Minigiant]

The main issue is that XCom like game have characters with single shots. So it makes sense to overwatch and hope for a shot at the target out of cover.

D&D is a multiattack game. So t's almost always better to attack multiple times over getting one slightly better shot. You have to address that first.