Zeno's Dichotomy Paradox, D&D Edition

[ermingarden]

probablybadrpgideas said "spell that halves your hitpoints but never kills you, a la zeno's paradox," and I immediately had to try to make that work. Here's what I came up with:

Zeno's Diminishing Dichotomies
5th-level Illusion

The target must make an Intelligence saving throw. On a success, the target takes no damage and the spell ends. On a failure, the target loses half of its current HP and must repeat the save at the end of each of its turns for the spell's duration. On a failure, the target again loses half of its current HP. On a success, the spell ends.

Damage from this spell can never take a target below 1 HP. If a target fails a save while at 1 HP, the spell does not end, but the target takes no damage from the spell that turn.

Components: V, S, M (a fragment of tortoiseshell)
Casting time: 1 action
Duration: Concentration, up to 1 minute
Range: Touch (in true Zeno fashion, be prepared to argue with your DM about whether it is in fact possible for anyone to actually touch anyone else, since the person approaching must first reach the halfway point between the two, etc., etc.)

Some thoughts:
- I made it an illusion spell because it's based on a paradox. I was thinking that it's an int save because the target is trying to see through the paradox...but since seeing through the paradox would, here, be realizing that HP is not infinitely divisible and thus it's possible to be killed, that doesn't make perfect sense.
- I think making it a 5th-level spell (in 5e) is fair because (a) there's no guaranteed damage on the first turn (unlike, e.g., Immolation, another 5th-level spell), so you risk burning your spell slot for no payoff; (b) it's a touch spell; and (c) legendary resistances severely limit its utility against really powerful targets. That said, I could definitely see an argument for 6th level. (The 3.5 spell Avasculate, a 7th-level spell which reduces the target's HP by half once, has the caster make a spell attack rather than the target roll to save and isn't a touch spell; you also get a lot more higher-level spell slots in 3.5 than you do in 5e.)

Thoughts? I'd love to hear any opinions on this or suggestions for improvement!