|Marvel Super Hero Squad TCG|
This may not seem like a big deal, but it is HUGE. -2 damage effectively will reduce many of your opponent's card to the point they are unplayable, nearly worthless. Why? Well, many effects trigger within two points of the maximum damage of the card. Other cards will simply have their damage reduced to the point that they're ineffectual. Why would I play a power level 7 double icon card if I'm only going to deal a maximum of 2 points of damage?
This is one of those cards that, on its own, would be very tempting to block even though it doesn't do massive damage. In a heavy green deck, this leaves your opponent open for more powerful green attacks later.
If this card's effect triggers, the end result is that it will likely force your opponent to pass their turn. This is where this card combines perfectly with a couple of the other Hero's Destiny cards - specifically, Spider-Woman's Come And Get Me and Arachnid Ambush. Both of these cards do damage to your opponent when they pass their attack, a condition that Back Off! is sure to bring about.
If you combined this card with Colossus's keeper, Body of Steel, that causes all of your opponent's cards to be -1 attack you can effectively shut your opponent's deck down, especially if they're relying on getting keepers into play.
A Colossus damage-control deck just got another great tool in its arsenal... and it's a COMMON!