This card is either really OP or really UP.
OP condition:
Lasts the entire turn, regardless of how many dragons are currently on the field, since at cast there were 0 dragons.
I will probably dump 5-6 dragons first turn, making Elements a total coin-toss game.
UP condition:
Lasts until the initial condition is no longer true
I will pay a card and 5hp for 1 dragon. Not worth it at all.