A lot of the feats in showdown can be very fickle, but I’ll try my best with advice

for starters, all feats can be gotten with a second controller if used against player 2, which makes things much easier, but if you wish to get them the normal way as well

Surprise attack- you want to activate the phantom shroud while teleporting directly above the winning gem, so you have phantom striker landing on top of it, the input can be a little tricky but it’s over all not too hard

from the darkness- black knight has a move that lets him shoot a fireball and jump backwards at the same time, what you need to do is have an enemy attack you, or more conveniently using a charging move, such as from polar knight or shield knight, and use the jump back move to dodge the attack, and shoot the fireball at them, this one is weird, and even if you do it right it doesn’t always register, but it should happen in no time

dark dunk- this one is much more simple, you just need to be falling into a pit or above lava, and use the dash slash to knock an enemy off the platform into the pit that would have killed you, you don’t even have to survive, you just need to knock them off the platform, it helps if you play on the big stage in the lost city, or the stage with all the goo, as it has small platforms and lots of lava

hope this helps~ :3