If you get Ronnie and the Professor (Martin), then i can't see them beating Count. It takes an entire Avengers team to take him down, and even then they only barely do it.
He's survived a phasing by the Vision, and even denied it.
Durable enough (understatement) for Thor's hammer to do nothing to him
Strength feat (can Firestorm get anything off before he creates a shock wave stronger than anything the Hulk can do?) If Jason is involved, how will he concentrate enough to transmute Count when this is continuously going on?
He has some energy absorption/control powers of his own
Nefaria has also discovered that he can control other ionic powered beings. Nefaria also apparently has a great degree of regenerative powers, as he was able to survive apparently being blown to atoms.
And he's quite fast, i do wonder if he could speedblitz Jason before they can transmute him, when looking at this.