Congratulations on making it to Pool 3! (Or just being curious, which is a great skill to have!)
Similar to the Start - Pool2 FAQ, this will cover FAQs and tips within Pool 3. Cards are once again, alphabetical, and Season Pass cards will be included, even before they hit Pool 3.
Pool 3 Cards
Agatha starts in your opening hand as a bonus card. This means you start the game with 1 extra card, and your deck to draw from is 1 card thinner. She will also ALWAYS choose to play herself, if able. Thus, if she plays Wave on turn 3, she will play herself on turn 4. Alternatively, if you are able to discard her (with say Lady Sif), you regain control of your plays for the remainder of the game. So long as she remains in her hand and cannot play herself, she will play essentially randomly, in regards to both cards and lanes chosen.
Pretend for a moment that this card said "Place the top card of your opponent's deck on the bottom of their deck." This would not be a good card. That said, outside of 1 specific interaction (Ronan), that card would be better than Mordo is, because Mordo still gives your opponent the option to play the card, or in fact, you may give them a 5 or 6 mana card, which when set to 6 cost, is not impactful. Even Yondu is a better card outside of Ronan, and he is not considered to be good in general.
Additionally, realize that for every time you had a good outcome (turn 2, they drew their Mr. Negative from it and had his cost set to 6), you've had another game with a bad outcome (they drew Mr. Negative on turn4 only because you made them draw their Magik and set her cost to 6 on turn 2 or 3). With no knowledge of where the critical card is, you are equally likely to help them draw that card on time as you are to remove it. And there are plenty
Finally, realize that even with the Ronan plan, a 2/5 (giving Mordo credit for +3) is solid, but even that has a cost associated as you are potentially helping them (giving them more options, and the cost of 6 may not be a significant increase).
Cerebro decks are cool and fun, but this is mostly a warning that there are a lot of locations that uninteractively mess with power. Wakandan Embassy is perhaps the worst, as it has nothing to do with its specific lane, but makes cards entirely unplayable for the deck.
Yes, you can redraw the cards you already had in your hand. Depending how many cards you had in your hand, you are often decently likely to do so. If you really want to play her, try to ensure you have a small hand on turn 4, or whenever you play her.
If you and your opponent both have a Daredevil on the field, this will not trigger. [Bug was fixed that if you had 2, it would not work]
Targetting is entirely random. He is happy to target a unit in a lane protected by Armor or whatever else and fail to destroy.
She will draw cards that have an adjusted mana cost of 0. This includes a Swarm that has been discarded and shuffled back into the deck (with Lockjaw for example) or an Iron Man that has been inverted by Mr. Negative.
If your opponent has 3 cards in his lane on turn 6, he can still kill more than 1 unit. Pretend your opponent played 5 cards in other lanes and you played Aero into Kingpin's lane. She will pull all 5, one at a time. The pull will happen. Then the kill will happen. Then there is a free slot to rinse and repeat until all are dead. Likewise, if Magneto sees multiple targets, he can kill as many as he wants, given there is at least 1 free space.
This only counts as Staging a single card, but that results in Playing 3 cards in essence. You can play this card if Sandman is on the field (and all 3 copies will go out). If Bishop is on the field, he will get +1 power from each Mysterio for a total of +3. The 2 clones have no ability, even once they are revealed at game end, so Patriot and Washington D.C. will both benefit them.
If you ever play him into Sinister London or Cloning Vats, or return him to hand with Beast, the new copy will be the mystery clone and will not change on game end at all (even if you placed the real one into London, for example).
Just realize that Agatha is a 6drop, and you are as likely to hit her as any other 6drop you want. She could negate you from playing the 6drop you got and wanted as well as your turn6 draw that could be said card.
He will kill in the same order they were played (or appeared in the lane) in. This can cause power to be different when a given unit is killed than how it appeared. Pretend for example that a lane has an Ant-Man and 2 other units in it. Ant-Man will get the +3 power when it sees Venom enter the lane. If Ant-Man was the first unit played there, it will be a 4 power unit when Venom eats it, resulting in that amount for Venom. If Ant-Man was the 2nd unit played there, he will die without his Ongoing active and result in only 1 power for Venom. There are several other ongoing effects that can have similar interactions.
This should read "Until the end of the next turn, cards in both player's hands cost 4." It is a subtle difference, but it can impact things such as Lady Sif or Colleen Wing if they are played on the same turn (and Wave is revealed first, due to initiative or play order). Furthermore, if Sakaar is revealed on a turn 1, all cards will cost 4 for the duration of both turns 1 and 2, meaning neither play can play any cards on those 2 turns.
Finally, aura-like cost adjustments will reapply AFTER Wave's On-Reveal has been applied. This means Sera will lower the cost of cards to 3. This is quit relevant, as a player with Sera in play can still play 2 cards on turn 6, while the player without Sera in play is limited to 1. Furthermore, Death will have her cost reduced from 4 rather than 9. This means if there have been 2 destructions this game, a player can play both Death (for 4 - 2 = 2 mana) and a 6-drop (for 4 mana) on turn 6, after Wave was played on turn 5.