Oh man, where do I even begin.
Martial Outlaw + Final Fang = you can reliably apply Heavy Bleed in PR and get a constant source of regen.
Martial Outlaw + Dark Pony = Marie's charge attack in general is very good, so the amount of meter you gain is quite insane. Add some Meter gain moves, and you have BB3 almost always up.
Prism Plumage + Unfazed = Easy access to thorns
Rose Tinted + Maid of Honor + Unfazed = Back when I stared out, this combo helped me grind PFs and PRs. You become quite tanky, and when you get low you either get regen from the Barrier + Maid or just from the amount of Miasma you're getting.
Pickle + Rogue Agent = Very unga bunga playstyle
Spellbent + 2x Noble Mogul = You gain barrier so fast, that you get the 300% damage increase quite fast. Her base damage is low, but the % damage + the Mobul increase makes her a very good critless fighter.
Rockstar Combos = all of them. Biting Cold, Corrosive Agent, Buffer Zone, Nyanotech, etc...
Windswept + Prism Plumage = immediate Evasion allows you to snowball quite hard.
Poltergust + Starlight Rose + Noble Mogul = Infinite BB3 spam
Wave Warrior + Starlight Rose + Noble = crap ton of damage
2x Harlequin + any Peacock = constant projectile spam
Trigger Happy + 2x Peashooter = Extremely easy wins during the early game. Scales terrible into the late game, but still fun
Big Top + Megalomaniac = Big Top regens HP so easily, and has a revive, allowing Megalo to get her Armor stacks quite fast
2x Evergreen Evil + Hex Calibur and Unfazed = extremely long precision/Miasma
2x Sundae or 2x Octo + UHost = extremely long Curse that also heals you
Prism + Gravedigger = immediate SA activation
Surgeon General + Gravedigger = reliable source for SA activation
Timeless hero + Starlight Rose = round start SA2 activation
Corrosive + Maid of Honor = great on offense vs Painwheel. Just spam BBs and soak up the damage
Harley + Peakshooter + any Umbrella = tons of burst damage if you go for Bubble spam
There are probably more, but these are at the top of my head