Spacial Rend has Base 100 power, while Dragon Pulse has 90. Spacial Rend has 95% Accuracy as well as high CH ratio, whereas Dragon Pulse has perfect accuracy. Draco Meteor has 90% accuracy but base 140 power and the stat drop. Competetively, Spacial Rend looks like a mid-party alternative between the two extremes to me. I also find that the "legendary signature move" part is a borderline flavour argument. I support that it stay allowed.
I also support Mist Ball as being allowed. People wouldn't be using it for the power, but for the chance of crippling CAP 8's special counters. It does score SE hits on Rev and Fidgit, as well as Arghonaut, but the latter is still hit harder by STAB T-bolt. So it doesn't add much coverage-wise as well as taking up a moveslot. It becomes a matter of choice for the user.
Selfdestruct and Explosion for Unallowed. They are too versatile in terms of countering counters.
I think that Focus Punch and Superpower should be moved to Controversial. One move is a TM and the other a Tutor move, so it won't hurt the movepool too much, and their viability is already subject to debate. I personally see their potential usefulness, and would like to see a vote take place.
True,
Spacial Rend isn't much more powerful, but with 15 extra BP(with STAB included), it could potentially change the game, but moreso, what's the point? Do you just want to make CAP8 more powerful in useless ways or actually add useful moves to the movepool. The movepool is limited, and as a legendary-exclusive move I don't see why we need to put it on this CAP. Also, same with Mist Ball, but not for the power reasons. Why do people keep wanting to add exclusive moves. They should just make a ban on exclusive moves, they're exclusive for a reason and certain Pokemon should be allowed to keep their special moves. What if one day something like Blissey, Vappy or Swampert got Water Spout or Eruption? They would all get a large boost in power, and the fact is they already have enough. If you want, make
Psychic allowed since it's a very common special move, but no exclusives, please.
Focus Punch should be controversial, but
Superpower unallowed, as it will likely OHKO(I haven't ran the calcs) TTar, one of it's major counters and there isn't a reason why CAP8 should have it.
Stop with the flavor and art arguments. It has never mattered for any CAP, and will never matter now, just get over it. It doesn't matter if CAP8 is a gigantic three headed cloud or a tiny worm. It'll still get the same moves, stats, everything.
All
Fire/Water moves should be allowed. Fire only hits steels, and they will wall CAP8's annoyingly if CAP8 doesn't get them, besides Scizor/Foretress/Metagross/Lucario, nothing really worthwhile is KO'd, and it gives CAP8 a better chance vs. Celebi. Water hits the pesky Grounds that will otherwise bash CAP8 all over the place, and isn't going to be an OHKO move on all but the most fragile of grounds(Dugtrio maybe) and gives CAP8 good coverage.
Really, it comes to this. Do you want a ridiculously easy to wall CAP8 who relies solely on it's STAB moves, or do you want a versatile CAP8 who has options with it's 1-2 coverage moves which can fight back to it's counters. Unless CAP8 gets Focus Blast/Aura Sphere, which is extremely unlikely and it shouldn't get Superpower, then things like TTar, Blissey and Snorlax will easily be a hard counter to CAP8 regardless, and there a lot of checks and revenge killers against CAP8, so i don't think we need to make CAP8 any weaker by giving it only one coverage move option. If CAP8 gets Calm Mind or another stat up move, a lot of sets will use it apart from the Choice sets and limit the coverage moves to only one, which will usually be a choice between Fire, Water or maybe Focus Punch, and will make people think twice before switching to any ground or steel type they have in their team. Giving CAP8 a reasonable amount of options rather then just limiting it to Surf or Fire Blast is unreasonable and will eventually make CAP8 a weak threat.