Wampa Stacking (Furious Foe)

I'm not sure but I assume it wouldn't until he roars again

I wouldn't mind seeing Wampa buffed with the following
Ability Text:

Inflict Healing Immunity on all enemies for 2 turns, which can't be Evaded. Wampa gains 40% Accuracy, 40% Critical Chance, 40% Tenacity, 40% Potency, and 40% Offense (stacking) for the rest of the encounter. Wampa gains 15% Turn Meter for each defeated ally and each active enemy. This ability starts on cooldown. (Cooldown 3)

No, it only stacks each time you use it

I understand we need to activate it every time, but the ability text is poorly written.

"...(stacking) for the rest of the encounter..."

For the rest of the encounter is to tell you the duration of the buff. If it says encounter then it only lasts for 1 phase of a raid for example.