First off, I think cards are AWESOME!!

I used this combo on KC Supes (who qualifies for both down his entire dial!) and it was down right nasty! (ICWO made it even more so.)

I tried it again with Magog and wondered if it could be used with Exploit Weakness and Charge. I am pretty sure it doesn't but just wanted to be sure.

Thanks in advance for the help.

No. Hold The Line requires a Power Action to use. Like HSS option 1, this makes it incompatible with just about anything except Super Strength and Steal Energy (both of which do not actually require their own action to use).

And Stay Down!, on the other hand, works anytime you make an attack roll while meeting the prerequisites.

Hold the Line might be fun on Black Hand (Justice League)