Is there anything that can bypass temporary hit points?


I have found a wizard spell from The Book Of Lost Spells, called Soul Shield. In my opinion, it is super overpowered, but my DM has allowed it.

The spell says that a wizard can convert their "real" hit points into twice as many temporary hit points, so long as you always leave yourself on at least 1 "real" hit point.

I instantly saw how amazing this was, however it leaves me wondering if there was a poison, disease, monster ability or the like that bypasses the buffer provided by temporary hit points and removes my remaining "real" hit point.
I have looked for such an ability, yet found none.

Is there one?

My DM likes to take things from homebrews quite a lot, so long as they are balanced, and I have had a look through a number of different sources. As such, a homebrew compendium is an acceptable answer for this question, but please link the source.

The spell in question works as follows:

Soul Shield

2nd Level abjuration

Components: VS
Casting Time: 1 action
Duration: 1 hour
Concentration: No

You siphon some of your life force into a shimmering shield of light around yourself. Sacrifice any number of your hit points (up to your current total -1) when you cast the spell, and you immediately gain twice as many temporary hit points. You must leave yourself at least 1 “real” hit point. While any of those temporary hit points remain, you get tactical advantage on Dexterity and Constitution saving throws. Remaining temporary hit points disappear when the spell ends. The spell ends immediately if all the temporary hit points are lost.