git gud. LOL ... I've always wanted to say that. but seriously, if you would have posted a roster it would have helped. the general rule of thumb is to have champs with high damage, immunity and power control. if you have champs in those three areas, you'll be just fine.
Save units and revives. Go in and do as much damage as possible, check before attacking to see if parry was shrugged off or not. Once he is below 55% health just hold block all the time and bait heavy to punish. If he uses SP you will die unless you have spider Gwen or Starky who can evade it, or Mr Sinister who can block it.
a couple things that i've learned while exploring the collector's quest: don't parry the collector until he becomes stun immune and then parry and re-parry as much as you can to mitigate the damage; turtle after doing a combo, take hits on the block baiting a heavy and punish it; if you see that the regen is too much just quit the fight and re-enter it ^_^
blade did great for me, just use him at the start of the fight so that you can still bleed the collector, and cap iw is good thanks to his high block proficiency. I don't know about guilly99 so i won't speak about her, but vision might have a hard time doing damage because of tenacity. Stealthy is good for the path, but like vision he will be hindered by collector's tenacity ^_^ If you have a White Magneto (even a 3* or a 2*) you could try with colossus: magneto's pre-fight ability turns your stun debuffs from parries into passive effects that can't be shrugged off, giving you openings to do damage (but that ability is currently bugged, so i would wait). Even if you don't have magneto i would still rank up colossus to R5, he is a beast ^_^
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If you have a White Magneto (even a 3* or a 2*) you could try with colossus: magneto's pre-fight ability turns your stun debuffs from parries into passive effects that can't be shrugged off, giving you openings to do damage (but that ability is currently bugged, so i would wait). Even if you don't have magneto i would still rank up colossus to R5, he is a beast ^_^
With your team I'd recommend minimum of 500 but 800-1k is advisable so you don't run out of units and get stuck at the collector.