Games like Highscore
Games like Highscore include Rogue Legacy 2, Broforce, SANABI, Contra: Operation Galuga, and Katana ZERO. We matched them by the tags players give Highscore on Steam (Action, Arcade, Platformer, Space Sim, and Side Scroller): closest matches first, and among equally close ones the better-known games.

Rogue Legacy 2
Shared: Arcade · Action · Platformer

Broforce
Shared: Action · Platformer · Side Scroller

SANABI
Shared: Action · 2D Platformer · Platformer

Contra: Operation Galuga
Shared: Action · Arcade · Platformer

Katana ZERO
Shared: Action · Platformer · 2D Platformer

SHINOBI: Art of Vengeance
Shared: Action · Platformer · 2D Platformer

Rogue Legacy
Shared: Platformer · Action · Side Scroller

METAL SLUG
Shared: Action · Arcade · Side Scroller

Gravity Circuit
Shared: Action · Platformer · 2D Platformer

Terminator 2D: NO FATE
Shared: Arcade · Action · Side Scroller

Streets of Rage 4
Shared: Action · Arcade · Side Scroller

METAL SLUG 3
Shared: Arcade · Action · Side Scroller

NINJA GAIDEN: Ragebound
Shared: Action · Platformer · Side Scroller

Shovel Knight: Treasure Trove
Shared: Platformer · Action · Side Scroller

BALL x PIT
Shared: Action · Arcade · Top-Down Shooter

Skul: The Hero Slayer
Shared: Action · Platformer · Indie

Huntdown
Shared: Action · Side Scroller · Arcade

Downwell
Shared: Platformer · Arcade · Action

Contra Anniversary Collection
Shared: Action · Side Scroller · Platformer

20XX
Shared: Action · Platformer · 2D Platformer

Volgarr the Viking
Shared: Action · Platformer · Arcade

Super Meat Boy
Shared: Platformer · 2D Platformer · Action

Pizza Tower
Shared: 2D Platformer · Platformer · Action

Bloodstained: Curse of the Moon
Shared: Action · Platformer · Side Scroller