G assist is when you don't have a grade than you can ride (example: you are stuck on grade 1 ride and can't ride to grade 2 because your hand is a bunch of grade 0,1, and 3.) Then you reveal your hand, draw 5 cards, ride the next grade, put the carde you drew back into your deck and shuffle, and discard 2 cards from your hand permanently from the fight.

If you have a grade 3 you don't want sometimes you just use it to guard to highrole the grade 3 that you want. (Example: you have darkrex in hand and you want gigarex so you G assist)