Temporary Hit Points...en masse?!

[Kae'Yoss]

I think they overlap, just like most other things. So if you have one false live, one vampire touch, and two aids, you have 4 different effects that grant you temporary HP. Track them all individually: if you sustain damage, subtract it from all sources (3 points of damage reduce each stack by 3). It the duration of one runs out, if the THP of one are used up or if one is dispelled, you still have the others.

 

[AuraSeer]

I don't think you can even overlap THP effects. That would be the same as stacking, because unlike most spells, THP can be reduced before the spell ends.

Say I receive two Bull's Strengths, for +2 and +4. They overlap, and only the strongest stays in effect, so my effective bonus is +4. If the stronger one gets dispelled, my bonus goes down to +2. Fine so far.

However, say I instead receive an Aid and a False Life, for 5 and 10 THP. They don't stack, so only the strongest one is effective and I have 10 THP. I then get hit for 10 points of damage, which should put me back to normal hp. But if the spells did truly overlap, then I'd still have the other spell giving me 5 THP! It'd be exactly the same as if the effects had stacked to 15 points, and then had 10 removed.

I think it's sensible to rule that only one set of THP can be in place at any time. If more than one effect grants you THP, the weaker one should go away entirely. (Only the THP component, though-- any other parts of the effect, like the +1 bonus from Aid, would work normally.)

 

[The Forsaken One]

Temp hitpoints don't stack, but they do overlap so you can attempt multiple casting to gain the most beneficial result.

ALl there is to say about them.

 

[Dr. Zoom]

However, say I instead receive an Aid and a False Life, for 5 and 10 THP. They don't stack, so only the strongest one is effective and I have 10 THP. I then get hit for 10 points of damage, which should put me back to normal hp. But if the spells did truly overlap, then I'd still have the other spell giving me 5 THP! It'd be exactly the same as if the effects had stacked to 15 points, and then had 10 removed.

If they overlap, you would have to subtract 10 from each THP effect you have in effect. In your example, you have 5 from one and 10 from another. You take 10 points of damage. Subtract 10 from both totals and you have none left.