Puzealth

Puzealth is the best 2d, ad-free and F2P (free-to-play) puzzle/stealth game.

Sneak through the level and collect orbs.
Collect the orbs to open the portal and complete the level.
Note: The game gets difficult when guards are on the post; avoiding them or assassinating them is entirely up to you!

Sometimes, assassinating them is the only option.
Master your stealth skills; you can always make a strategy by calculating the guard's position and timing to use against them.

The game is designed in a way that there is more than one way to clear each level.
So, it is up to you how you treat this game: as a puzzle game, stealth game, or strategy game.
It is about how you play it!