If anyone is looking for an easy way to get the 12000 damage and 10+unique hits trophies, here are the minimal effort solutions that worked out for me. There are obviously other ways to do it, but maybe these ideas will help someone out.
For the 10+ unique moves trophy, Muramasa's basic air combo should suffice.(Requires 1 meter bar) 2A>2B>2C>26B>jB>jC>(air)26A>jE>(air)26C>jC>(air)26AB. If all goes well, it should be around 21-22 hits and the trophy will pop up once the match is over.
Getting 12k damage the cheesy way (ideally with a 2nd controller). Pick Carol (bug swarm) and Angela (robot bombardment one) as assists. I went with Saya as the lead character. Build up 3 bar meter, wait for the assists to charge and put the opponent in a corner. Once this preparation is complete, summon up Carol, then Angela right away and wait for both assists to hit. Wait for the dmg counter to reach about 7500-9000 mark and then use Saya's ultra (2626BC). The outcome is a bit dependant on luck and timing, but this way you can deal 11-13k without learning complex combos.
P.S. Just need to clear arcade 4 more times and platinum =get :D!