I think you're going about this the wrong way.
The point of a burrower is the element of surprise, and from what you're describing of the worms basis, I think that rather than shoot off adds, you should go with something more visceral.
Have the damn thing erupt from the ground, bite down on an individual player during the burrowing phase, and have it apply a corrosive debuff or something for the duration of the biting down. Under certain circumstances, the player can be freed from the beasts maw and the raid continues normally, or...
And this is one I like
Make this kind of situation the red line attack style of the boss, and the only way to reliably finish it off as its shooting around like a meaty bullet train is to actually get inside the damn thing after getting bitten down on.
Once inside the belly of the beast, the player has a race against time to finish off the boss before the things digestive juices finish them off.
Keep the lightning and fire shit for the majority of the fight so that way it starts as a positioning heavy encounter, and then the switch to insane locomotive burrower serves as an excellent dosage of mood whiplash.
Er...Sorry if I came on a little strong there, but I think that kind of scene would have a lot more tension than random offsplitting of multiple heads or summoning of extra mobs. It'd also fit the behavior of a giant carnivorous worm more, I think.
The point of a burrower is the element of surprise, and from what you're describing of the worms basis, I think that rather than shoot off adds, you should go with something more visceral.
Have the damn thing erupt from the ground, bite down on an individual player during the burrowing phase, and have it apply a corrosive debuff or something for the duration of the biting down. Under certain circumstances, the player can be freed from the beasts maw and the raid continues normally, or...
And this is one I like
Make this kind of situation the red line attack style of the boss, and the only way to reliably finish it off as its shooting around like a meaty bullet train is to actually get inside the damn thing after getting bitten down on.
Once inside the belly of the beast, the player has a race against time to finish off the boss before the things digestive juices finish them off.
Keep the lightning and fire shit for the majority of the fight so that way it starts as a positioning heavy encounter, and then the switch to insane locomotive burrower serves as an excellent dosage of mood whiplash.
Er...Sorry if I came on a little strong there, but I think that kind of scene would have a lot more tension than random offsplitting of multiple heads or summoning of extra mobs. It'd also fit the behavior of a giant carnivorous worm more, I think.