Games like Seth Slays Everybody
Games like Seth Slays Everybody include Hades, Hades II, Skul: The Hero Slayer, Have a Nice Death, and Kingdom Rush - Tower Defense. We matched them by the tags players give Seth Slays Everybody on Steam (Tower Defense, Action, Strategy, Action Roguelike, and Roguelike): closest matches first, and among equally close ones the better-known games.

Hades
Shared: Action Roguelike · Action · Hack and Slash

Hades II
Shared: Action · Roguelike · Action Roguelike

Skul: The Hero Slayer
Shared: Action · Action Roguelike · Roguelike

Have a Nice Death
Shared: Action Roguelike · Action · Hack and Slash

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

Dead Cells
Shared: Roguelike · Action Roguelike · Hack and Slash

Tower of Babel: Survivors of Chaos
Shared: Action Roguelike · Action · Roguelike

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

Kingdom Rush 6: Genesis TD
Shared: Tower Defense · Strategy · Action

Lost Castle
Shared: Action Roguelike · Beat 'em up · Hack and Slash

Tangy TD
Shared: Tower Defense · Action · Strategy

Bloons TD 6
Shared: Tower Defense · Strategy · Cartoony

Orcs Must Die!
Shared: Tower Defense · Action · Strategy

Doom Sweeper
Shared: Tower Defense · Action Roguelike · Hack and Slash

Vampire Survivors
Shared: Action Roguelike · Roguelike · Action

Drill Core
Shared: Tower Defense · Strategy · Roguelike

The Binding of Isaac: Rebirth
Shared: Action Roguelike · Roguelike · Indie

Octogeddon
Shared: Action · Action Roguelike · Strategy

Death Must Die
Shared: Action Roguelike · Action · Hack and Slash

Hero Siege
Shared: Action Roguelike · Hack and Slash · Roguelike

Nordic Ashes: Survivors of Ragnarok
Shared: Action Roguelike · Roguelike · Strategy

Rogue Legacy
Shared: Action · Roguelike · Action Roguelike

Megabonk
Shared: Action Roguelike · Roguelike · Action

Risk of Rain (2013)
Shared: Action Roguelike · Action · Roguelike