Wizards and cowboys! That's a fun combination, liked the backstory :)
The game itself is pretty cool. the bosses have lots of variety, liked the minions a lot (cats are evil, I always knew that!). Small minions can be hidden by the bullets; making them and the character larger (while keeping the hitboxes the size they are now) would improve it in my opinion.
The music and SFX are fitting, the sprite designs are fun.
Because the game is about "cowboy-style strength proving", solely boss fights feel appropriate to me, with some dialogue and moving from one boss to the next there could be a short plot!
Thanks!