If you lose all Temporary HP from the Tenser's Transformation spell, does the spell end?

If you lose all Temporary HP from the Tenser's Transformation spell, does the spell end?

I played a game where I used an item that has the effects of the Tenser's Transformation spell. I know the spell lasts for 10 minutes. Since the effect came from an item, I didn't need to worry about making Con saves to maintain concentration on the effect when taking damage.

During the course of the combat, but before the spell's duration was over, all my Temporary HP from the spell's effect were used up. The GM said that the spell also stops when that happens. I could not find any mention of this in Xanathar's Guide to Everything. Is there any errata for this or an official ruling in the Sage Advice Compendium that proves or disproves this?

Any mention dealing with Temporary HP only states that if there are any remaining Temp HP left over after the spell expires, those remaining THP go away. I don't see anything as of yet saying that the spell/effect ends when THP runs out.

• Was the item a custom one, made by your DM, for example? Oct 26 at 7:46
• Yes, the game was to mimic Mighty Morphing Power Ranger in a D&D5e Setting with items that has Tensers Transformation as a once a day item a kin to the Morphers from the show. Oct 26 at 7:51
• I'm very confused about why this question is attracting downvotes. "My GM is citing this rule that I find questionable but can't find in the rules, where is it?" is a common question format. Oct 26 at 17:11
• @JhyarelleSilver Oh, so he's trying to mimic the thing where the Rangers get defeated and unwilllingly revert to their civilian forms? Oct 27 at 13:24

Losing the temporary HPs granted by the spell does not end it.

The description of the Tenser's Transformation spell states:

You endow yourself with endurance and martial prowess fueled by magic. Until the spell ends, you can’t cast spells, and you gain the following benefits:

[a list of cool things...]

Immediately after the spell ends, you must succeed on a DC 15 Constitution saving throw or suffer one level of exhaustion.

There are no special conditions that cause the spell to end: per the description, the caster can concentrate on the spell for up to 10 minutes, so the spell ends early only if the concentration of the caster ends. Since you said this spell has been cast from an item and does not require concentration, Tenser's Transformation lasts for the entire period of 10 minutes.

If the item is a custom one, the creator of the item may have added this further ending condition.

There is no official magic item which allows to cast Tenser's Transformation$$\^\dagger\$$: ask your DM if this further condition is specified in the description of the item.

$$\^\dagger\$$: to the best of my knowledge and after searching on D&D Beyond, trying to filter magic items using the menu for the "Attached Spell".