Games like Air Marty
Games like Air Marty include Undertale, OMORI, The Binding of Isaac: Rebirth, Hollow Knight: Silksong, and Cuphead. We matched them by the tags players give Air Marty on Steam (Indie, Dark Comedy, 2D, Multiple Endings, and Comedy): closest matches first, and among equally close ones the better-known games.

Undertale
Shared: Great Soundtrack · Multiple Endings · Indie

OMORI
Shared: Indie · Great Soundtrack · Psychological Horror

The Binding of Isaac: Rebirth
Shared: Indie · Replay Value · Great Soundtrack

Hollow Knight: Silksong
Shared: Indie · 2D · Great Soundtrack

Cuphead
Shared: Cartoon · 2D · Indie

Hollow Knight
Shared: Indie · 2D · Great Soundtrack

OneShot
Shared: Indie · Great Soundtrack · Multiple Endings

Reventure
Shared: Indie · Multiple Endings · 2D

Papers, Please
Shared: Indie · Multiple Endings · 2D

Geometry Dash
Shared: 2D · Great Soundtrack · Indie

Pizza Tower
Shared: Indie · Great Soundtrack · Comedy

Milk outside a bag of milk outside a bag of milk
Shared: Indie · Psychological Horror · Multiple Endings

KinitoPET
Shared: Indie · 2D · Psychological Horror

The Henry Stickmin Collection
Shared: Multiple Endings · Comedy · 2D

The Hex
Shared: Indie · 2D · Psychological Horror

DELTARUNE
Shared: Great Soundtrack · 2D · Comedy

Please, Don’t Touch Anything
Shared: Indie · Multiple Endings · 2D

Gunpoint
Shared: Indie · 2D · Comedy

Class of '09: The Flip Side
Shared: Dark Comedy · Comedy · Multiple Endings

The Stanley Parable
Shared: Indie · Comedy · Multiple Endings

Monster Prom 2: Monster Camp
Shared: Indie · Comedy · Multiple Endings

Dialtown: Phone Dating Sim
Shared: Indie · Comedy · Psychological Horror

NEEDY STREAMER OVERLOAD
Shared: Psychological Horror · Multiple Endings · 2D

The Binding of Isaac
Shared: Indie · Replay Value · Great Soundtrack