In regards to Adol's Classic Mode, how about the following fights
1. vs. Robin (alt 1) on Adol Stage (Omega Form) (Dark Fact; Ys I Final Battle)
2. vs. Zelda (alt 6) & Giant Robin (alt 1) on Adol Stage (referencing fight vs Zava; after being defeated Giant Robin spawns referencing Dalles; Ys II)
3. vs. Giant Ridley (alt 2 or 4) on Mushroomy Kingdom (Omega Form) (referencing the fight against Sol-Galba; Memories of Celceta)
4. vs. Marth (alt 5) on Castle Siege (referencing the fight against Chester; Oath in Felghana)
5. vs. Giant Greninja (alt 1), Giant Bowser (alt 2), Ridley (alt 5), and Giant Palutena (alt 3) (referencing the fights against the Warden Psyche bosses in Ys VIII)
6. vs. Ike (alt 3) & three mini Pits (alts 2, 3, and 5) on Frigate Orpheon (Omega Form) (referencing the fight against Ernst and his three homunculi; Ark of Napishtim)
7. vs. Chrom (alt 5) & Palutena (alt 3 or 5) on Spear Pillar, or Reset Bomb Forest (Omega Form) (referencing the fights between Scias, and later Tialuna; Seven)
Bonus = same old, same old
Final Battle = Galeem (referencing the fight against Darm at the end of Ys II).
This is what I could come up with within this hour, give or take.
(I know that there are a number of fights that repeat fighters but, just couldn't think of better matches for said fights
).
EDIT:
NoOtherPersona
just gave me an idea!
How about, fighting against all Sword Fighters? (Link, Marth, Roy, Ike, Shulk, Corrin, Hero (four skin types)). It could go something like:
1. vs. Young Link, Toon Link, and Link (in that order; the next appearing after defeating the former; referencing the timelines)
2. vs. Marth & Roy (referencing their appearance in Melee)
3. vs. Ike (both young, and mature skins)
4. vs. Chrom, Lucina (referencing Fire Emblem Awakening)
5. vs. Shulk
6. vs. Cloud
7. vs. Hero (all four different skins; appearing in order of series; III, IV, VIII, XI).
Bonus Stage
Final Battle = vs. Demon King Ganon