if the yoshi is dumb enough to use all the jump going towards the opponent pikachu can just utilt
and if the yoshi goes for the edge usmash dsmash and bair work
and if the yoshi is even more dumb a simple downb from pika stops yoshi most of the time
also, you can try to be a bit clever and hit them when they downb you will get knockback and damage but if done correctly yoshi loses its second jump and simply falls usually downb near edge you can also knock yoshi out of its downb animation without getting hurt