I’m guessing the PI team here is busy working on the to-be-released update for PI, so there may or may not be a slew of feedback for a day or so.
As far as what you want to do, I sense your enthusiasm for getting started on doing such an effect, but ya gotta get to learn PI a bit first to pull it off. This because you may have to use two layers for this effect using two different emitters.
I don’t have the time to go and look these up for you, but if my memory is correct, you could use one of the cloud-type explosions for the mushroom head part — one that oval-ish, and one that is an up-moving fire-swirl type one together.
While the new PI update will give you the ability to download emitter libraries automatically and keep them current, if you haven’t done so yet, go get all the emitters so far (“all_emmiters Part 1” and 2) on the Wondertouch page.
Then go cruise through them and look for the emitters mentioned (probably in explosions and clouds type sets — which are in several emmitter libraries).
If/when you find the two types I stated, put the cloud one on the top layer and the firey swirl un the second (beneath it). Then use the tutorial, etc. to learn how to tweak them to make them work together.
Hope this helps to some extent.