I cast Armor of Agathys, gaining 10 Temporary hitpoints, and I do 10 hp of cold damage when .

Then a friendly wizard casts Bear's Endurance on me, rolls 2d6 and grants me 12 temporary hitpoints.

How would you rule?

Quote from Mog_Dracov >>

I cast Armor of Agathys, gaining 10 Temporary hitpoints, and I do 10 hp of cold damage when .

Then a friendly wizard casts Bear's Endurance on me, rolls 2d6 and grants me 12 temporary hitpoints.

How would you rule?

 

 

 

 

 Direct quote on temporary hit points:

Healing can't restore temporary hit points, and they can't be added together. If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 temporary hit points when you already have 10, you can have 12 or 10, not 22.

This information would prove that the bears endurance would not add to the armor agathys, since you cant accumulate temporary hit points.

Quote from Smokehorn_knight_of_Cats >>

Quote from Mog_Dracov >>

I cast Armor of Agathys, gaining 10 Temporary hitpoints, and I do 10 hp of cold damage when .

Then a friendly wizard casts Bear's Endurance on me, rolls 2d6 and grants me 12 temporary hitpoints.

How would you rule?

 Direct quote on temporary hit points:

Healing can't restore temporary hit points, and they can't be added together. If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 temporary hit points when you already have 10, you can have 12 or 10, not 22.

This information would prove that the bears endurance would not add to the armor agathys, since you cant accumulate temporary hit points.

 
To go a step further than what Smokehorn_knight_of_Cats stated, if you opt to take the 12, it replaces the 10 from Armor of Agathys as per the RAW that Smokehorn excerpted. The description for AoA states:

A protective magical force surrounds you, manifesting as a spectral frost that covers you and your gear. You gain 5 temporary hit points for the duration. If a creature hits you with a melee attack while you have these hit points, the creature takes 5 cold damage.

So, RAW, if you take the 12 you lose the cold damage. If you keep the 10 THP, then you do 10 cold damage per attack until you take 10 damage and lose “those” specific THP.

So, RAW, it would be an answer not included in your poll. That answer being: 

“That depends, did you accept the 12 THP from Enhance Ability, or did you opt to keep the 10 from Armor of Agathys?

Thanks, that is very helpful.