I've been searching an answer to my doubt among the existintg threads but I didn't find it, so here we go:
Imagine your hero is, for example, a Half Goblin and the Dungeon Lord rolls 1 goblin + 2 potions. You use your special ability to transform that goblin into a thief, and then you use that thief to quaff both potions.
Will you have to discard both two new members of the party at the Regroup Phase? Only one of them? None of them?