From what I've seen in a deck where rabblemaster is the only goblin and with the elementals that sac themselves rockslide is at least on par with rabblemaster especially when facing other aggro decks the card becomes especially insane in one game versus a boros tokens deck it wa able to get to a 10/10
This is a fair point, I feel like Rockslide Elemental may take too long to get up and running though. The deck has the potential to make it huge with all the tokens and Unearth creatures available, that is for sure, and it IS an Elemental for Master.
I just don't know if it is worth it. Rabblemaster starts swinging in for usually around 3-4+ the turn after it is played, which really helps with a deck like this that is really relying on getting there fast. Rockslide will almost never be in a position to trigger Evolve on Raptor, and most of the time I would rather be playing other things that either do, or put the opponent on a significant clock the following turn when it can start attacking in immediately. It also is yet another card in the deck that will fold hard to bounce. Someone Bouncing an Evolved Raptor to remove all the counters can slow the deck down considerably, and Rockslide suffers from the same problem, while also lacking real evasion and being more expensive to initially cast.
Rockslide also pushes the deck to wanting to play it before your Unearth creatures to get the most out of them (getting a +1/+1 counter vs. not). This means either waiting till after T3 to play them (in which case you may be gimping Raptor) or playing out the game plan as usual and just accepting the loss of value.
I will say that in the testing I did Rockslide DID make an excellent blocker because of First Strike. Something this deck tends to lack (since most of the time everything you have you want to be attacking with when possible rather than blocking or otherwise get saced when they block so you don't want to be blocking too often). This may have some merit. The issue I have with this though is that since the deck is already so "all in" on attacking every turn possible, I think it is probably just better to keep with the theme rather than trying to run cards that are effective blockers (aka Rabblemaster vs. Rockslide).
On that note, I am considering messing around with a card I had used in my old Izzet Unearth+Evolve build.
Phantasmal Dragon. A 5/5 with evasion for 4 isn't terrible, even with the Illusion targeting weakness. It triggers Evolve well, and contains
to help enable Devotion pretty well also. Again the big issue here is that weakness to removal.
The decks biggest weakness overall is that many of the more threatening cards the deck runs tend to be pretty weak to bounce and cheap removal. Combine this with Unearth creatures not sticking around and you end up with the potential to stall out at times. Even Rabblemaster tends to have this issue, but I feel like Rockslide and Phantasmal Dragon both tend to be a little softer than Rabblemaster because of their weakness to bounce.
I know the weakness inherent to the deck could be worked out, but I feel like for something like this they are sort of worth the risk. Running cheap threats like Raptor and creatures that don't really do much to progress your board position (Unearth) certainly makes the deck stall out at times, but it also has the potential to get there off very little.
An opening hand of Raptor+Hellspark+Brackwater is often enough to get there by itself, with no other interactions or cards being spent, assuming Raptor doesn't eat removal within the first 2-3 turns.
T1: Island, Raptor.
T2: Mountain, Hellspark, trigger Evolve (Raptor becomes a 1/2), attack for 4. Opponent at 16.
T3: Any Basic Land, Brackwater, trigger Evolve (Raptor becomes a 2/3). Attack for 2. Opponent at 14.
T4: Unearth Hellspark, trigger Evolve (Raptor becomes a 3/4), attack for 10. Potential 2 mana still open, opponent at 4.
T5: Unearth Brackwater, trigger Evolve (Raptor becomes a 4/5), attack for 8. Potential 2 mana still open, opponent at -4.
A potential T5 kill off of 3 total mana and 3 total cards isn't anything to sneeze at. Especially when we are running stuff like Shock and Vapor Snag to help push that damage through with that extra mana we have open.
Early cheap removal and an abundance of bounce can certainly pose an issue, but I think it is worth it for the potential it has when it gets to do its thing unfettered.