It might sound repetitive, but just as
@bbp said, try to invest in your offense. Lacking in Attack power is sometimes the main reason to fail a 3 minutes match.
But if you can´t hit the opponent hard enough, try to play in a smart way. Many variants might help you out.
Triller Squigly can decimate the HP of a team in one minute ONLY tagging them out (I play her with 3 tag out movs). Xenomorph can play suicidal to give 3 stacks of permanent bleed to the oponent (And valentine can bring her back just to... die again), or you can play extra chessy with her/his doom.
Filia might find problems with Valentine Variants because her close relation with bleeds, but if you´re lucky and you have her, Filia Class Cutter if well invested, can make her stop regenerating with HEAL BLOCK if you hit her good, and if you use LEECH marquee, you can heal pretty well the damage you could recive from BB usage.
Squigly´s Inferno of Leviatan is also a great way to give her heal block and WITHER (5% less of bb meter per second) to keep her bb3 away a day. Or just combo her down to death only
Squigly has an amaizing super long combo vs bigbands, what could prevent Dreamband to hit the ground and win inmunity/reset his buffs timers.
Model Leader:
Very weak to: Cerebella and Beowulf Throws. Bad Hair day Filia, Xenomorph, Djiin Frizz Filia with 5 stacks of enrage bb3´s. Eliza Red velvet (But be aware that she moslty have tons of HP investment, so she might take away her SA, but be really hard to decimate).
Assassin's Greed:
Very weak to: Not use BB´s at all (Like Roge Agent Ms Fortune), Wulfsbane, Terror bite Robo Fortune.
Splitting Image: Very weak to: God?... Hacks? (No, just a jokeeee! please don´t now I´m sad meeee!! ToT), Window cellphone throwing?, Uninstalling the game? Naaa, just use a bad hair day with the firt cut and a valentine final stand support, let her hit you a little bit and then counter to perma bleed her to death. Squigly Jackson and Xenomorph works fine with her too. Also, hitting her with a well invested attack diamond brings her down.
Hope this helps a little!!