I'm not going to argue that pandemonium isn't good in those decks, but I would like to point out that none of those combos are exactly game breaking.
I admit I don't pvp that often, but I don't think I've
ever encountered an opponent using a pandemonium deck. I have tried it myself and with some success, but none of the decks you can build around this card are extreme powerhouses.
Simply put pandemonium
can do lots of damage, but you can't
count on it doing damage. Usually at least one of the possible effects on a given creature will be at best useless, and sometimes out and out counterproductive.
(ever reverse timed your opponent's entire field when you're trying to deck them out?)
As to the decks jmdt mentioned:
Pand + voodoo doll -> gravity pull and bblood + voodoo is just flat out a better deck. it's only effective if you have your entire field full of voodoos, which means a trio so you can get fractal. Very card intensive for not a lot of payout.
Creatureless stall->
has no spell that can damage the other player, and discord doesn't deal huge amounts of damage, so unless you're decking them out you need at least a duo. Stalling with a
duo doesn't actually work well. Bone wall might get along get with pand, but vulture and boneyard don't really, so most of the time you're better off using plague.
In mono
deck-outers reverse time is hugely counterproductive and you can't count on taking out dangerous creatures. Usually it seems like just antimattering the scariest thing on the field would be better.
Immortal decks-> Flying glories doesn't really sound workable, you need a duo (trio technically, but no
is needed) and a lot of
stalling wouldn't get along with pand. (none of the shields available work well in a
/
duo)
/
is workable (or at least it holds it's own in pvp1), but nothing to write home about. For the most part what keeps you going there are the phase shields, not pand.