Luck is fun to play with in RPGs. Let’s do the same thing with spell DC!
Drawde’s Everchaning Enchantment
1st-level enchantment
Casting Time: 1 action
Range: Self
Components: V, S, M (a copper coin)
Duration: Instantaneous
Choose a spell of 1st level or lower that you can cast, has a duration of instantaneous, and requires a saving throw. You are considered to have cast that spell. Roll a d4 and a d20. If you rolled even on the d20, add the d4’s result to the spell’s save DC. If you rolled odd on the d20, subtract the d4’s result from the spell’s save DC.
At higher levels. If you cast this at 2nd level or higher, increase the spell level that can be cast by 1 for each level above 1st.
Thoughts?
Throat Punch Games 
This would be cool as a low level Eldritch Invocation for warlocks. As a spell, I can’t see why one wouldn’t just try this all the time, but I like it anyway! good stuff.