at least a skull shield, i think.
well, considering 30 dmg from malignant cells, sundial 6 turns, even with the poison stacking, you would possibly lose.
the nymphs aren't necessary-----> 1) if according what u say, cc the creatures and sundial. what's the point if you can just sundial and prevent the damage.
2) by the way you mention it, you r ignoring the dmg of higher hp creatures until they turn into malignant cells and flood the field.
3) by the way it looks, what screw opponents isn't cc but poison dmg. looks to me the nymphs are just for display purpose apart from clogging the hand cards.
and i'm sure....since you mentioned something like Jenkar's deck,
1)you have missed something essential in the deck.
2)it's meant to counter some deck and not for general usage. it might be possible since it screws the opponents chances of placing high dmg creatures/ growing creature with low hp. and i would have put plague