Shroomisaur looks like an interesting concept for sure, I don't know why I hadn't considered the possibiliy of trickscarf on something as nimble as this. It's a shame you're not strong enough to OHKO bulky Volc or Gorebyss though, I would consider reducing the attack EVs down to 168 since you still get the OHKO on offensive Volc and the 2HKO on Gorebyss and you free up a bunch more EVs for bulk. You also still OHKO Offensive Starmie 100% of the time after LO and SR if you end up coming in on Rapid Spin, Ice Beam easily OHKOs you however. The extra bulk from 184 HP makes you a better check to Excadrill since +0 Rock Slide now has basically no chance to 3HKO you, especially if you trick it and get some leftovers.
I may end up having a play with this set later, if that's the case I'll probably post some more thoughts then.