Games like Monster Mayhem
Games like Monster Mayhem include Vampire Survivors, Skul: The Hero Slayer, The Binding of Isaac, The Binding of Isaac: Rebirth, and Rogue Legacy. We matched them by the tags players give Monster Mayhem on Steam (Action Roguelike, Action, Roguelike, 2D, and Cute): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Action Roguelike · 2D · Roguelike

Skul: The Hero Slayer
Shared: Action · Action Roguelike · Roguelike

The Binding of Isaac
Shared: Action Roguelike · Roguelike · Action

The Binding of Isaac: Rebirth
Shared: Action Roguelike · Roguelike · Indie

Rogue Legacy
Shared: Roguelike · Action Roguelike · Action

Hades
Shared: Action Roguelike · Action · Roguelike

Have a Nice Death
Shared: Action Roguelike · 2D · Action

Enter the Gungeon
Shared: Action Roguelike · Roguelike · Indie

Megabonk
Shared: Action Roguelike · Roguelike · Action

Dead Cells
Shared: Roguelike · Action Roguelike · 2D

Sephiria
Shared: Action Roguelike · Roguelike · Action

Risk of Rain (2013)
Shared: Action Roguelike · Roguelike · Action

暖雪 Warm Snow
Shared: Action Roguelike · Roguelike · 2D

BALL x PIT
Shared: Action · Action Roguelike · Roguelike

Cult of the Lamb
Shared: Action Roguelike · Cute · 2D

Dungreed
Shared: Action Roguelike · Roguelike · Action

Nuclear Throne
Shared: Action Roguelike · Roguelike · Action

Rabbit and Steel
Shared: Action Roguelike · Roguelike · Cute

Hades II
Shared: Action · Roguelike · Action Roguelike

Spelunky
Shared: Action Roguelike · Roguelike · 2D

Halls of Torment
Shared: Action Roguelike · Roguelike · Action

Death Must Die
Shared: Action Roguelike · Action · 2D

Ravenswatch
Shared: Action Roguelike · Roguelike · Action

Octogeddon
Shared: Action Roguelike · Action · Roguelike