I don't think adding Antimatter is a good idea, but in my opinion it's need a bit buff.
If that's need an Antimatter, the Chaos seed need too. And after that, nobody will use Antimatter (becomes UP), because "Why I pay 8 for this, if I be able to use for 3 and a little risk." Why little? If somebody uses Antimatter, have quanta to use Pandemonium twice. And I didn't seen any unburrowed/material field, what can survive an attack like this. Because in 20-80%(matters on the creature) you always have a good option take that creature out of the field. And it's raisen and doubled... I don't think, that's the best way to buff this card.
Why this card is unused? In my opinion (that's not mean, I'm right, because I'm newbie
):
I, Because the upped is more weaker than the other cards updated edition. Rain of fire, Plague, Skull buckler. They are not as effective, like the upped Pandemonium (and I think, can't race with the unupped), but they are more reliable. And I don't want everytime, to kill a 20 creature table, only 1-3 of them. It's often kills the half of the creature (so 1 or maybe 2). And for 5, I think, that a very high price for one upgrade card (Siphon life,Fire lance...).
II, The upped part are weaker than the unupped in some ways. There are a lot of deck, what's often rely on to deal damage his own creature too (or just doesn't give a shhhh.....). Woodoo dolls, burrowed/imma creatures or controlls with empty field... And these decks doesn't ever want to upgrade this (pay more to less efficiency), if it's needed, they change the card for an other. Only some kind of Rainbow controll and mono full upgraded entrophy deck not (if it's doesn't use upped Antimatter instead of that). But it's lucky based and cost so much (that's why the Chaos seed is not unused, because it's very cheap in any view, but I hate the upped part of that, because that's not the same card in my eyes).
III, What if the infection (and only the infection) affects on imma creatures too? Because noboydy are safe from the Chaos
I know, it can make troubles in the programming of that card (I think the Panda just skips the imma creatures, cos this is the logical). Or the infection changes to Alfatoxin (of course, WITHOUT Malignant cells)? Or the Lobotomize dealt 1 damage too? I thought about to decrease the upped by one, but it's could be too much, and can becomes OP in a very fast way.
I think, this card is not have to be much stronger, than the older one, but needs a bit help.