Games like The Protean Forest
Games like The Protean Forest include Slay the Spire, Balatro, Slay the Spire 2, Monster Train, and Monster Train 2. We matched them by the tags players give The Protean Forest on Steam (Deckbuilding, Roguelike, Card Game, Card Battler, and Turn-Based Strategy): closest matches first, and among equally close ones the better-known games.

Slay the Spire
Shared: Card Game · Roguelike · Deckbuilding

Balatro
Shared: Roguelike · Card Game · Deckbuilding

Slay the Spire 2
Shared: Roguelike · Deckbuilding · Card Game

Monster Train
Shared: Deckbuilding · Card Battler · Card Game

Monster Train 2
Shared: Roguelike · Card Game · Deckbuilding

Inscryption
Shared: Card Game · Deckbuilding · Card Battler

Vampire Crawlers: The Turbo Wildcard from Vampire Survivors
Shared: Deckbuilding · Card Battler · Roguelike

Wildfrost
Shared: Card Battler · Card Game · Deckbuilding

9 Kings
Shared: Roguelike · Deckbuilding · Strategy

Touhou: Lost Branch of Legend
Shared: Roguelike · Card Battler · Deckbuilding

Dicey Dungeons
Shared: Deckbuilding · Card Battler · Roguelike

Infinity Wars: Animated Trading Card Game
Shared: Card Game · Deckbuilding · Strategy

Marvels Midnight Suns Digital Edition
Shared: Deckbuilding · Turn-Based Strategy · Turn-Based Tactics

As We Descend
Shared: Card Game · Roguelike · Card Battler

DICEOMANCER
Shared: Card Game · Card Battler · Deckbuilding

Roguebook
Shared: Deckbuilding · Card Game · Roguelike

FrostBound
Shared: Deckbuilding · Roguelike · Card Game

Die in the Dungeon
Shared: Roguelike · Deckbuilding · Card Game

Library Of Ruina
Shared: Card Game · Deckbuilding · Strategy

Magic: The Gathering Arena
Shared: Card Game · Deckbuilding · Strategy

天外武林 (Traveler of Wuxia)
Shared: Deckbuilding · Roguelike · Card Game

Dungeons & Degenerate Gamblers
Shared: Roguelike · Deckbuilding · Card Game

LONESTAR
Shared: Roguelike · Card Battler · Strategy

My Card Is Better Than Your Card!
Shared: Roguelike · Deckbuilding · Card Game