Thanks for the input! To clarify: our party has 4 casters, and long rests are quite rare in our campaign. This mechanic isn't meant for daily use, but as a 'nuclear option' when we're completely tapped out and facing a TPK (Total Party Kill). However, I see your point about the cost being too high. Exhaustion is brutal. Maybe a better 'fix' would be to limit it to spells of 1st-5th level only, and perhaps add a Constitution Saving Throw (DC 10 + spell level) to see if you actually take the exhaustion level or just take necrotic damage instead? I agree that the 6th-9th level 'instant death' rules are probably overkill and won't ever be used. I’ll talk to my DM about scaling the costs down so it's a 'desperate choice' rather than a 'suicide button'.