Games like Skirmish Mayhem
Games like Skirmish Mayhem include BALL x PIT, Megabonk, Deep Rock Galactic: Survivor, 20 Minutes Till Dawn, and Brotato. We matched them by the tags players give Skirmish Mayhem on Steam (Action Roguelike, Action RTS, Bullet Heaven, Bullet Hell, and Shoot 'Em Up): closest matches first, and among equally close ones the better-known games.

BALL x PIT
Shared: Action Roguelike · Bullet Hell · Roguelite

Megabonk
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Deep Rock Galactic: Survivor
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

20 Minutes Till Dawn
Shared: Action Roguelike · Bullet Hell · Shoot 'Em Up

Brotato
Shared: Action Roguelike · Bullet Hell · Bullet Heaven

The Spell Brigade
Shared: Bullet Heaven · Action Roguelike · Bullet Hell

Soulstone Survivors
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Nova Drift
Shared: Bullet Hell · Action Roguelike · Shoot 'Em Up

Yet Another Zombie Survivors
Shared: Action Roguelike · Bullet Heaven · Top-Down Shooter

Halls of Torment
Shared: Action Roguelike · Bullet Hell · Roguelite

Nordic Ashes: Survivors of Ragnarok
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Tower of Babel: Survivors of Chaos
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

R.I.P. - Reincarnation Insurance Program
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Rogue: Genesia
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Vampire Survivors
Shared: Action Roguelike · Bullet Hell · Roguelite

Death Must Die
Shared: Action Roguelike · Bullet Hell · Bullet Heaven

Necrosmith
Shared: Action Roguelike · Bullet Hell · Roguelite

Vital Shell
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Arms of God
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Tiny Rogues
Shared: Action Roguelike · Bullet Hell · Top-Down Shooter

Apocalypse Party
Shared: Action Roguelike · Bullet Hell · Top-Down Shooter

Time Wasters
Shared: Action Roguelike · Bullet Heaven · Bullet Hell

Nuclear Throne
Shared: Action Roguelike · Bullet Hell · Roguelike

NIMRODS
Shared: Action Roguelike · Bullet Heaven · Bullet Hell