shuffle your hand into your deck.then draw 7 cards.you cant play any more trainer cards for the rest of your turn.

now lets say you are playing a stall deck.your opponent and you have very few cards in your deck.you have a very large hand.you use pro.elm and put your hand in your deck.then you draw 7 cards.now you have a much larger deck than your opponent and if you keep stalling he/she will deck first.