Games like Mage Mountain
Games like Mage Mountain include Monster Train, Slay the Spire, Slay the Spire 2, Balatro, and Wildfrost. We matched them by the tags players give Mage Mountain on Steam (Card Battler, Turn-Based Tactics, Deckbuilding, Roguelite, and Perma Death): closest matches first, and among equally close ones the better-known games.

Monster Train
Shared: Card Battler · Roguelite · Deckbuilding

Slay the Spire
Shared: Card Battler · Deckbuilding · Card Game

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

Balatro
Shared: Deckbuilding · Card Game · Roguelike

Wildfrost
Shared: Card Battler · Turn-Based Tactics · Card Game

Inscryption
Shared: Card Battler · Deckbuilding · Card Game

Griftlands
Shared: Card Battler · Deckbuilding · Roguelite

9 Kings
Shared: Deckbuilding · Strategy · Card Game

As We Descend
Shared: Card Battler · Deckbuilding · Turn-Based Tactics

LONESTAR
Shared: Turn-Based Tactics · Card Battler · Strategy

Roguebook
Shared: Deckbuilding · Card Game · Roguelite

Trials of Fire
Shared: Card Battler · Turn-Based Tactics · Roguelite

StarVaders
Shared: Turn-Based Tactics · Deckbuilding · Roguelite

Dicey Dungeons
Shared: Card Battler · Deckbuilding · Roguelite

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

Dream of Corpse Lady
Shared: Card Battler · Turn-Based Tactics · Card Game

Super Fantasy Kingdom
Shared: Roguelite · Strategy · Deckbuilding

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

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

Vault of the Void
Shared: Deckbuilding · Card Battler · Roguelite

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

Loop Hero
Shared: Deckbuilding · Roguelite · Roguelike

Cross Blitz
Shared: Deckbuilding · Roguelite · Card Battler

Monster Train 2
Shared: Deckbuilding · Card Game · Turn-Based Tactics