Question

I think:

Hydro Pump: Piplup doesn't have that great of Special Attack, so the higher power is needed.

Ice Beam: A good move as always.

Aerial Ace: Mostly for Mud-Slap, but also can take down Grass types when Ice Beam runs out of PP.

Mud-Slap: Once again speaking of Mud-Slap...

Answer 1

My suggestion:

Surf-more reliable than hydro pump.

Ice beam-Covers those grass types.

Aqua ring/agility/yawn-A good support move will help. Yawn is good to either get a sleeping foe, or force a switch.

Mud slap-cheap move, most of the good electric types have low defenses, so this can do a bit of damage, while protecting piplup with low accuracy, of course, you'd probably switch out Piplup anyway.

Answer 2

That is a great moveset trachy but becuase mud slap sucks why not tm dig I just check it is compatable.

and surf is much more reliable than hydro pump.