Since I did a review for Clobber's sister card, Impede, I felt I should do one for Clobber as well, especially since I've seen this card in a frankly worrying amount of decks posted/discussed. Clobber is a bad card. I just wanted to get that out there first because apparently it needed to be said.
Since the game first started, the idea that damage/thwart/ect... is worth a certain amount of resources has been discussed in great detail and a consensus of two damage for one resource being generally accepted (essentially Spider Man's Swinging Web Kick is the poster child for this). This might have actually been a rather high bar to set at the time when cards like Haymaker and Upper Cut were some of the only cards out there but now a days it's very easy to hold to this standard or even surpass it with a card like Mean Swing.
All of that set up to say, Clobber fails this basic ratio test badly. At standard cost you're spending three resources for three damage. This is Haymaker levels of bad... Haymaker, wow. But wait, it comes back into your hand if it's the first card you play a turn! Doesn't that make up for it? And the answer is still no. Even at a "refunded" two resources for three damage the card is still too weak to see play on its own merits in a generic capacity.
Which leaves us with the last reason that this might see play: synergies. Clobber can be used and then held for next turn to be used again every turn for the rest of the game. Of course, at that point you're no longer getting your "refunded" cost and you're stopping yourself from drawing a new card each turn but technically this is potentially valuable. At the time of this review the only character that specifically cares about having an attack event to play every single turn is Gamora (and maybe Spider-Woman to a lesser extent, but it's much worse with her than Gamora).
Frankly, Gamora has far far too many better options of cards to put into her deck for her to ever want something as weak as this. Even if we add the value of her base ability and her sword to the effect of Clobber (plus one damage and thwart) the card only breaks even(!) on what it's expected value for cost should be (three resources for four damage and one thwart). Yes, even with a three cost upgrade and hero ability buffing it, it still only just breaks even...
I don't know what more to say. Frankly this review really shouldn't even need to be written. I'd have thought this would all go without saying and yet Clobber is still being put in decks (as a three of no less!) and still being mentioned when discussing top Aggression cards and that just boggles my mind.