Sentinels of the Multiverse is a great game which understands how to make co-op fun. However where SotM understands how card games work and makes decisions from there, The Cauldron understands how SotM works and adds to and improves the base formula. This set is worth a buy if you love Sentinels. Now let's talk about why Quicksilver is a great hero
If it wasn't obvious, Quicksilver is an expy of Wolfverine with the powers of the T-1000. This is fiting, since she hits like a truck and is very hard to put down. Her main gimmick is that her deck is full of combo cards and they all have the same effect that you can immediately play a finisher after or hit herself for 2 melee damage to chain another combo card. The combos tend to deal small damage but can stack up quickly (much like Matriarch's birds). Combine this with cards in her deck that increase her own damage or the damage of everything on the field or the card that lets you play combos during the enemy's turn and you got yourself a force to be reckoned with
She has her share of weaknesses, and sadly they're pretty glaring. Aside from the obvious "she hurts herself" thing, her main one is she suffers from "why can I only play one card a turn?" syndrome. Yeah, she can play multiple combos and a finisher on top of that, but you'll have to choose between that and the card that prevents her from hurting herself or that lets her draw more cards. So much like the Knight and Tango One you'll have to put infliciting damage aside for a few turns while you set her up. Additionally she'll need a lot of cards in her hands to consistently pull off combos, and you'll burn through your hand just as quickly. To make matters worse she has an inferrior base power to Malichae, who gets to see the cards he draws before he decides on what to discard. And speaking of powers, she doesn't really have any in her deck. Her only real power is a heal that only works if she didn't inflict damage, so you'll be relying on your cards to inflict damage. Also be careful with her reforming armor─while it does provide her a lot of survivability, if she gets hit when she only has one Hp1 left, she'll be down for the count. So don't rely on that too much!
Despite all these weaknesses, Quicksilver is a very powerful hero that can tear through enemies quickly once she gets set up. You won't be doing a who lot until she is, though, so pair her with heroes like The Stranger to let her get cards out faster. It will take a while for her to get going, but once she finally does just try to stop her while remianing in one piece.