It is a threat in its own right and it is a combo piece but also just a very good card
Thankfully the oracle text is more clear on such cards, and we have two great examples to demonstrate this
We still get the occasional call to bring back tuck, but those numbers continue to dwindle
If it features Pokemon species the Pokemon cards on the back will be Fire Energy, Charmander, Rattata, a back image of a card, Potion, Machop, and a Fighting Energy the art with only energy cards shows one Pokemon card back and Grass, Fire, Water, Lightning, Psychic, and Fighting energy cards
Theyre action at a cost, and you start getting into logjams where you cast your learn card, then cast the Lesson, then draw more learn cards in the process, and have more spells than you have mana to cast them