I've found that it's better to use 3 Quintessences (and drop the Dimensional Shield), you want your "fallen druid+firefly queen+elite otyugh" to stay in game permanently.
I'm not a huge fan of rain of fire in this deck (it is situational at best, and if you are eating everything possible with your othughs anyway you don't need it), but thanks to the elite firefly queen you should have a lot of fire quanta, you might want to consider fire bolts etc.
On the other hand if you have a miracle or two, you might want to add them to your deck, with a normal firefly queen.
I second the graveyard-boneyard idea, you need the skeletons to put them back into your deck (with eternity) or to mutate them with your fallen druid, they shouldn't stay out long enough to make a difference.