Need a Sixth for Elite Four

I need a final pokemon for my team against Elite Four.

My team thusfar:

Lucario-Lvl. 60
Item:Lucarionite
Power-Up Punch
Swords Dance
Aura Sphere
Bone Rush

Delphox-Lvl. 60
Item:Mind Plate
Mystical Fire
Physic
Psyshock
Flame Charge

Aurorus-Lvl. 60
Item:None
Ice Beam
Ancient Power
Avalanche
Aurora Beam

Blastoise-Lvl. 60
Item:Blastoisnite
Aqua Tail
Water Pulse
Water Gun
Skull Bash

Yvetal-Lvl. 60
Item:None
Snarl
Oblivion Wing
Foul Play
Dark Pulse

I need one more and also can you critique my team.

You should consider adding Talonflame, if you could. Preferably, one that has Gale Wings ability. With this and Brave Bird, you could wreck through any opponent without any sort of trouble at all. I know you already have a fire-type Pokémon on your team already, as well as flying, but you're not playing competitively, though, this is an in-game team, so it shouldn't hurt.

You seem to lack something against Water types. I recommend a Grass type, like Trevenant or Ferrothorn. You could also go with Florges, because it can learn Grass type attacks despite being pure Fairy.

Thanks. I actually beat it adding a Druddigon and teaching Fennekin grassknot and Aurorus Thundershock.

I'd also recommend some different moves for Blastoise. You should replace Aqua Tail, Water Gun, and Skull Bash with moves like Ice Beam, Focus Blast, and Flash Cannon.

Trevenant would be a great choice