How does your submission match the theme?
Your health is also your ammo
WASD is move/aim/use item
Weapons also heal you on pickup
Destroying the crystal stops monsters from spawning and gives you items

Third-party resources
Created in Gamemaker Studio
Sfx from http://sfbgames.com/chiptone/
Room transitions using https://marketplace.yoyogames.com/assets/2291/transition-system

Contributors
Music done by John Schmit
Aside from third-party resources all were done by myself
Feedback/testing done by friends: michael, kfuzz, singalong, taloxi, sisune, John Schmit