I play with Anther like... a lot. So I've gotten a lot of experience in this matchup >.< unfortunately I play him a lot.
If you're aggressive against a smart pikachu (so far, only Anther's pika beats mine), they're going to easily out-maneuver you and ****. You have to be smart with a lot of things. They key here is... SERIOUSLY... don't get impatient!
They're going to stand in their shield and wait for you to make a mistake by hitting it or just in general misspacing, because it is REALLY easy to misspace against a pika. Stand your distance, ftilt them, throw waddles. If they attack you and your shielding, they can attack you faster then any other move in your arsenal can come out (even grabbing), so always wait for that second attack and make your move.
A thing that everyone I've ever played has fallen for is if you hit someone with a 1-2 jab, and then proceed to the third constant jab, they don't move out of it for a while... netting a lot of damage. Then afterwards, leaving it out, people ALWAYS run into it. It's funny, but also a good defense. A lot of moves with huge priority (luigi's nair) will still get hit by this, leaving you to then let go while they are in the air and do whatever. Moves with disjointed hitboxes (Ness's moves, Lucario's, Marth's) will clang with the hammer and Dedede will be lag free.
Player tendencies taken into account, after ftilting someone, they'll simply have to jump. And they're either going to jump on top of you or away. If towards, utilt. If away, waddle them. They have to, there's no other way to punish ftilt (maybe a few, but I can't think of any). Just an observation of how good ftilt can control space.