Butcher is a pixel-art 2D shooter, but don't let that fool you: it's brutal. Seemingly taking a page out of the Brutal Doom rulebook, everything in this game bleeds more profusely than it really needs to, and make no mistake, there are a lot of things in Butcher that bleed. You play as a cyborg sent to Earth in order to destroy all remaining human life... you get the picture. There's also meat grinders and swearing.
Anyway, if that takes your fancy, GOG is currently giving it away for free as part of its Made in Poland sale (the game was made in Poland, you see). At the time of writing the offer has just over 38 hours to go, so you'd be well-advised to snap it up quick.
Once you've got it, look forward to a fast, reflex-oriented shooter with 20 levels and a whole lot of grim weaponry. You can also paint each level with blood, because of course you can, though there's a 4 million pixel ceiling.
As for the other games made in Poland, that sale features highlights like Frostpunk, This War of Mine, Ancestors Legacy and God's Trigger, as well as The Witcher series, obviously. You'd do well to check it out. There's a trailer for Butcher below: