Games like MUMMMASTER!
Games like MUMMMASTER! include Plants vs. Zombies GOTY Edition, Kingdom Rush - Tower Defense, Bloons TD 5, Bloons TD 6, and Cat Goes Fishing. We matched them by the tags players give MUMMMASTER! on Steam (Cats, Dark Humor, Tower Defense, Side Scroller, and Spectacle fighter): closest matches first, and among equally close ones the better-known games.

Plants vs. Zombies GOTY Edition
Shared: Tower Defense · Casual · Zombies

Kingdom Rush - Tower Defense
Shared: Tower Defense · Casual · 2D

Bloons TD 5
Shared: Tower Defense · Casual · Action

Bloons TD 6
Shared: Tower Defense · Casual · Singleplayer

Cat Goes Fishing
Shared: Cats · Casual · 2D

Mewgenics
Shared: Cats · Dark Humor · 2D

Your Only Move Is HUSTLE
Shared: Spectacle fighter · Action · Side Scroller

ASTLIBRA Revision
Shared: Side Scroller · Spectacle fighter · 2D

Kingdom Rush Origins - Tower Defense
Shared: Tower Defense · Casual · 2D

ICEY
Shared: Side Scroller · Action · Spectacle fighter

Kingdom Rush Frontiers - Tower Defense
Shared: Tower Defense · 2D · Casual

MARVEL Tōkon: Fighting Souls
Shared: Casual · Spectacle fighter · Action

Rock 'N' Roll Defense
Shared: Tower Defense · Casual · Action

Until We Die
Shared: Side Scroller · Tower Defense · Action

One Way Heroics
Shared: Side Scroller · Mystery Dungeon · Dungeon Crawler

Stickman Trenches
Shared: Side Scroller · Tower Defense · Action

Cult of the Lamb
Shared: Dark Humor · Dungeon Crawler · 2D

South Park™: The Stick of Truth™
Shared: Dark Humor · Action · 2D

Dungeon Tycoon
Shared: Tower Defense · Dungeon Crawler · Dark Humor

pureya
Shared: Casual · Side Scroller · 2D

Happy Wheels
Shared: Dark Humor · Casual · Action

Utopia Must Fall
Shared: Tower Defense · Casual · Dark Humor

Grim Nights
Shared: Tower Defense · Side Scroller · 2D

Cat Quest
Shared: Cats · Action · Casual