One I came up with was Plasma, Poison, and Explosion.
Plasma+Explosion - can petrify and deals 20% more damage
Plasma+Poison - The poison clouds can be charged wth plasma creating a zone of dot.
…Poison clouds already have a DoT. The point of this interaction is to take over someone’s poison cloud so that it deals damage to everyone but the plasma user. It doesn’t make the clouds stronger, however plasma does deal 10% more base damage on contact with someone poisonned.