Ridley vs Pikachu

You might just want to pick a different character for this. Matchup is almost impossible unless you can pull out some cheese

Ridley's only advantage against Pikachu is that he can kill Pika early. Pikachu is difficult if not impossible to edge guard because of quick attack, and Ridley's size makes him combo heaven.

Pray. Just pray that the enemy SD's the whole game.

When pikachu is trying to get up, use neutral b to spam him. That way, pikachu will continually gain damage without getting to you. Then once he's at a high enough percent, use a smash attack to kill