ASSASSIN'S GREED VALENTINE
SA1: When the opponent uses a BLOCKBUSTER against Valentine, they lose 25% of their remaining HEALTH and suffer HEAVY BLEED for 5 seconds.
SA2: Gain 5% HEALTH per second while nearby an opponent suffering BLEED.
1. No blockbusters (yet)
She can be overpowered with low-combo, heavy damage attacks. For example, Harlequin Cerebella would be great with frequent special moves. Stay away from characters that rely on blockbusters, like Big Band.
2. No bleeding
Pick a character that can get IMMUNITY. Either via signature ability or special move (Squigly, Peacock, and Parasoul have taunts). Or use a Valentine with a "ICU" marquee ability (Valentine gains HEAVY REGEN for 20 seconds when suffering a DEBUFF).
Essentially if she can't make you bleed, then go ahead and blockbuster (if you can spare the health). The regen she gets from your bleeding is the biggest thing to worry about.