Great card... it practically fits into any deck, it's like "IronHeart" but better, since it activates when it comes into play instead of when it comes into play from your hand... Just remember to put a support that has the resource you can get the most to need ("Ipac" if you want mental "Utopia" if you want physical "DangerRoom if you want electric) If one day a support with universal comes out even better.
Some X-men allies, Rockslide included, don't seem to be that good for the cost. 4 is a very high cost to merely hit twice for 3 and go down against a villain attack or swing one last time. But you have to remember that a lot of the X-men allies are not great for the cost to begin with. The reason lies with the impressive amount of synergies they have with things like the Training upgrades and Danger Room. Insert Rockslide alongside these 2 and you suddenly have a 9 HP ally that can deal 12 damage over 4 turns AND take a villain hit before finally being discarded. Doesn't even need a med team for that value. There is no easy-ish way to do this with non-Xmen Protection allies with other traits.
Another great way to play Rockslide is with Mutant Protectors, in which case you cheat him on the board at 1 cost and defend with him. At 6 HP he can comfortably take a villain hit without getting removed most of the time with the added bonus of 1 Retaliate. You can then use him to attack or defend again the next turn, which can be quite good at 1 cost.
The target of the game is to knock out villain. This card gets insane value (1 ER per 5 damage) which is superior even to the hero specific events. However there is a small "but". First you need to reveal treachery. It can be something, that's automatically end your game. The harder scenario you play, the more dangerous this card is.
Summary: (A-C): B- in standard/easy scenarios C+ in rest.
This is not a hero action, so Phoenix and Psylocke can use this is alter ego. This is an amazing card to use against stalwart/steady enemies. Drop down to AE, let the villain scheme, and you basically have a confuse and thwart in one card.
This doesn't seem like a great card, but I can see some use for it in Psylocke justice decks. Psylocke with Heroic intuition can get 4 THW and if the villain is confused his card would do 5 damage with Floating like a butterfly. Seems pretty good attack for justice aspect and requirement of basic thwart is quite easy too.