#1: Kazuya, because he's the protag of the first SMT. Primarily summons Pascal.
#2: Demi-Fiend, protag of the epicest game. Uses the epic stronk attacks and has Dante in his final smash.
#3: Raidou Kuzunoha, popular spin-off character. Does Raidou things.
#4: Removal of Joker, because he is lame and shilly. DLC completely deletes Joker from the game and turns everyone that plays as them online into Sans.
#5: Frost ace, an epicer variant of Jack Frost. Has ice attacks and a sword.
#6: Yu Narukami, the spin-off king. Has a real moveset and not some dumb gimmicky summon gauge thing.
And, finally, spirits
Set 1: Kazuya's mom, Law Hero, Chaos Hero, Female Hero, Thorman (evolves into Thor, man), Gotou, Lucifer, Metatron
Set 2: Matador, Trumpeter, David, Riders, Lucifer
Set 3: Never played Raidou, probably Lucifer
Set 4: All Persona 5 spirits removed, add Lucifer
Set 5: Jack Frost(evolves into Black Frost), King Frost, Demonee-Ho, Frost Five, Raiho, Lucifroz
Set 6: Every Persona 5 spirit's P4 equivalent