Games like Idle Monster TD
Games like Idle Monster TD include Tower Wizard, Cookie Clicker, Zero Stress King: Idle Defense, Idle Champions of the Forgotten Realms, and Shelldiver. We matched them by the tags players give Idle Monster TD on Steam (Strategy, Tower Defense, Idler, Pixel Graphics, and Fantasy): closest matches first, and among equally close ones the better-known games.

Tower Wizard
Shared: Idler · Strategy · Fantasy

Cookie Clicker
Shared: Idler · Pixel Graphics · Incremental

Zero Stress King: Idle Defense
Shared: Tower Defense · Idler · Strategy

Idle Champions of the Forgotten Realms
Shared: Strategy · Idler · Fantasy

Shelldiver
Shared: Idler · Resource Management · Incremental

(the) Gnorp Apologue
Shared: Strategy · Idler · Incremental

Kingdom Rush - Tower Defense
Shared: Strategy · Tower Defense · Fantasy

Plants vs. Zombies GOTY Edition
Shared: Tower Defense · Strategy · 2D

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

Crusaders Quest : Hero Town
Shared: Idler · Pixel Graphics · Fantasy

Nodebuster
Shared: Strategy · Idler · Incremental

Bloons TD 6
Shared: Strategy · Tower Defense · Casual

Chef Knight
Shared: Strategy · Idler · Incremental

Dragon Cliff
Shared: Strategy · Idler · Pixel Graphics

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

Dungeon Warfare
Shared: Strategy · Tower Defense · Pixel Graphics

Relic Guardian - Tower Defense
Shared: Strategy · Tower Defense · Pixel Graphics

Incredicer
Shared: Idler · Strategy · Incremental

Kingdom Rush 5: Alliance TD
Shared: Strategy · Tower Defense · 2D

Rusty's Retirement
Shared: Idler · Pixel Graphics · Automation

The King is Watching
Shared: Tower Defense · Strategy · Fantasy

Timber Rush
Shared: Idler · Strategy · Casual

Tiny Pasture
Shared: Idler · Pixel Graphics · Cute

Factorio
Shared: Strategy · Resource Management · Automation