Ask Sakurai to nerf (I mean pichu has been falling off lately and is the lightest in the game)
Disjoints are your best friends
Go for kills earlier, since Pichu's glaring weakness is being a lightweight.
Pichu has a very small hurtbox and can be annoying to deal with.Use downtilts more that side tilt and use range whether it is projectiles or a fat hitbox to your advantage
Pichu's recovery(Up B) has no hitbox so when off stage predict where pichu is going to be and attack or even better, spike pichu
Pichu can't deal with opponents with very large hurtboxes.(E.g Ike's Nair)Since pichu doesn't have the range to deal with stuff space pichu out.
Pichu has one of the worst disadvantages in the game if the opponent is a stock higher than them.But also has the strongest advantages in the game (If the opponent has a stock less than them). Pichu's game plan is rather aggressive so let the pichu go for you then after they attack punish.