There are a couple of tactics that I follow when I take on X-Force and TGT. My basic approach is to deny green and black primarily, and blue secondarily. What you don’t want to have happen is for X-Force to down one of your three characters, because a Power Surge after that will inevitably result in a game over. Likewise, it’s rare to recover from a Surgical Strike. I keep an eye on the opposition’s green AP; if an X-Force is about to go off, I make sure I rotate a character to the front that can soak the damage.
The first priority target for me is X-Force, since he’s faster to take down. TGT is powerful, but it’s rare for the AI to get the Power Surge/Smite combination running in the correct order, and a Smite by itself should be soakable too. Once X-Force is down, I switch to denying red and blue, and it’s usually game over.
If X-Force drops a Recovery tile, best to match it away and take the damage, than give him more time to build up for a more damaging attack.
The other component is picking your matchup well. If you’re running an exclusively 3* team, it’s important to try and select out an opponent that’s running a loaner featured character. There are too many HP to take down, if the featured 3* is maxed, and too high a risk of having the featured 3* get enough AP for an ability in a colour you can’t prioritise.
The team I tend to run is LThor/BP, with +3 G/B boosts, and +3 R/Y boosts (+/- +3 to all AP boosts, depending on how high my score is, and how quickly I’m going to need to make the hop). It provides me with a useful outlet for the colours I’m denying, and a CtS/RoTP is usually enough to down X-Force and the loaner, leaving me only TGT to deal with (although it’s arguable whether Defence Grid is actually a useful power).
Obviously, you can still fall victim to a bad board, or a nasty cascade, but that’s how it goes.