I think you are right about the body slam thing. Maybe those cards should just end up in a stack? Because if you just go and body slam everything the run changes dramatically (in a negative way).
I think what I am thinking as upgrades an extention of the current perk system. Additional perks to get in a play through. Both neutral perks which can be acquired by a anyone. And maybe perks that can be acquired by specific classes (upgrades to started perks?) and of course patchy if it has the necessary starter perk.
They can alter the game dramatically or just change some stats. Like:
Neutral:
Double damage to poisoned enemies
Burning enemies drop scrap
Fire spreads
Stun enemies who attack you
Higher town spawn
Higher item spawn
Higher gold spawn
Turn all health pods to dentures
Caves always contain good things (spelunk)
Slimes heal (acquired taste)
Aliens are friendly and more alien spawn
Ninja:
1 move without losing combo
Infinite combo in low health
Cowboy:
Enemy reaction time +1 turns (fastest in the west)
+1 damage
etc.
I will send you the en.json it's not done yet but perhaps I can work on it more once there is support for it.