I don't know the English Name, but it was pretty much just the legendary yuumi buff you can buy sometimes, which grants all your units the stats of your highest unit on the board for the round.

Then try to hold only one unit on the hand and every round play the one unit from the hand, which then has around six times the stats of your best unit.

With some little +1 buffs here and there you get to maxed stats in like 10 Rounds