How to combine states or ailments?

I seek help and guidance adding combined states to my game!
I wanted to do something different with my ailments system, a thing of those somes is the capability to combine ailments.

For example, you have the states Asleep (Can't act, takes extra damage but recovers HP) and Afraid (may act and loses MP every turn). The moment an actor or enemy has both they automatically turn into the state Nightmare (Can't act, takes extra damage, loses HP and MP every turn).

My problem is that I don't know jack about scripting and therefore don't know where to even begin.
I have most of Yanfly's battle plugins, so I should write the custom effects in the state's notes? Should it be something in the base troops? Is another way that my overreliance on plugins has blinded me from?

Anyway, any advice helps and is appreciated.

How many combinations will there be? Looks like it could be accomplished attaching a common event to the Skill that applies the state, then having the common event check for certain existing states on the skill's target.

I don't know the exact number. The idea is recent, but the total number would be like four.
Three (Nightmare, Freezeburn, Plague) of them made out of two base ailments and one (*Name pending*) made out of three.

And what would the commands for that common event would be? I tried, but I don't know anything about scripting so I haven't been able to make it work.