Sylveon is impressive. Before evolving Eevee to Sylveon, have it learn Trump Card at level 45. Pixilate gives TC's last use have 390 BP.
There's also Heliolisk (especially in sunlight), Gengar is best if you train it in E12 and breed Sludge Bomb and Thunderbolt via Stunfisk>Grimer>Gengar, there's Chandelure (especially in Trick Room)(E12: Energy Ball via Petilil/Lotad>Phantump>Chandelure), Exeggutor in Trick Room (E12: Sludge Bomb via Grimer>Phantump>Exeggcute), Reuniclus (especially in Trick Room)(E.Ball the same way as with Chandelure), Roserade (E12: Sludge Bomb and Extrasensory via Grimer>Phantump>Exeggcute>Roselia (not Budew), also give it Technician as Ability and Hidden Power), Clawitzer (E12: Ice Beam via Remoraid), Ampharos in Trick Room, Shell Smash Omastar, Flogres, Empoleon (E12: Ice Beam, Scald and Agility via Panpour(Scald)>Buizel(Agility)>Remoraid(Ice Beam)>Piplup), Liligant, Nasty Plot Crobat, Nasty Plot Houndoom...
...would be some that haven't been mentioned by others yet (or just great movesets for already mentioned ones).