Games like Helvetii
Games like Helvetii include Skul: The Hero Slayer, Hades, ICEY, Rogue Legacy 2, and Vampire Survivors. We matched them by the tags players give Helvetii on Steam (Action, Indie, Adventure, Side Scroller, and 2D): closest matches first, and among equally close ones the better-known games.

Skul: The Hero Slayer
Shared: Action · Indie · 2D

Hades
Shared: Indie · Action · Roguelite

ICEY
Shared: Action · Side Scroller · Adventure

Rogue Legacy 2
Shared: Action · Indie · Adventure

Vampire Survivors
Shared: Indie · 2D · Roguelite

Rogue Legacy
Shared: Indie · Action · Singleplayer

SANABI
Shared: Action · Adventure · Indie

Streets of Rage 4
Shared: Action · Indie · 2D

Dead Cells
Shared: Adventure · 2D · Roguelite

The Vagrant
Shared: Action · 2D · Side Scroller

Dust: An Elysian Tail
Shared: Action · Indie · Adventure

Monster Boy and the Cursed Kingdom
Shared: Action · Adventure · Indie

Hollow Knight
Shared: Indie · 2D · Singleplayer

Mark of the Ninja
Shared: Indie · Action · 2D

Hades II
Shared: Action · Roguelite · Mythology

Dungreed
Shared: Action · Indie · 2D

Zombotron
Shared: Action · Adventure · Indie

Hollow Knight: Silksong
Shared: Indie · 2D · Singleplayer

God of War
Shared: Action · Adventure · Singleplayer

鬼谷八荒 Tale of Immortal
Shared: Singleplayer · Action · Mythology

Dungeon Munchies
Shared: Action · Indie · Adventure

ScourgeBringer
Shared: Action · Indie · Adventure

Deadlight
Shared: Action · Indie · Adventure

UnderMine
Shared: Indie · Action · Roguelite