If I have Miltank with the "Moomoo Malt" Ability as my Active Pokemon and I use Welder to attach 2 Fire Energy cards to a Benched Pokemon, does it heal 90 or 180 damage?
Any energies attached from the hand would trigger Moomoo Malt, once for each energy card being attached. So in this case you would heal 180 damage.
Source: TPCi Rules Team (2019-05-09)

Relevant cards

Note: All applicable cards may not be listed below.
SM10_189
SM10_189
SM10_189A
SM10_189A
SM10_214
SM10_214
SM4_78