For Safety Goggles, I've seen them put to great use as bait for Breloom's Spore, especially for 'mons Breloom has a tough time beating otherwise. Metagross/Gyarados/Salamence, for example, can set-up or outright KO non-sashed variants as he attempts to Spore them.
Roserade is a great offensive anti-Breloom choice as well, as it resists Breloom's two STABs and ignores Spore, while OHKOing back with Sludge Bomb. It's reliant on Hidden Power for coverage but Grass/Poison hits a lot at least neutrally anyway.
I've got half of my team bred up for this competition (I just spent yesterday getting two of them bred, thankfully I don't have to cross-breed across egg groups for anything else >.>), still trying to decide on a proper Mence check though. Might go for Donphan after all, Rapid Spin is non-existent and Adamant 252 attack Ice Shard doesn't care if Mence has set-up already.
Those are good points about 'Gross, Gyara and 'Mence actually, I might have to give them a try!
I'm not so sure on Donphan as a revenge killer though, the 2hko from Ice Shard isn't guaranteed (unless you have Never-melt Ice), and you'll be taking a fair chunk of damage in return:
252+ Atk Donphan Ice Shard vs. 0 HP / 4 Def Mega Salamence: 80-96
(47 - 56.4%) -- 71.5% chance to 2HKO
252+ Atk
Never-Melt Ice Donphan Ice Shard vs. 0 HP / 4 Def Mega Salamence: 92-112
(54.1 - 65.8%) -- guaranteed 2HKO
252 Atk Aerilate Mega Salamence Return vs. 0 HP / 252 Def Donphan: 87-103
(52.7 - 62.4%) -- guaranteed 2HKO
252 Atk Aerilate Mega Salamence Double-Edge vs. 0 HP / 252 Def Donphan: 102-120
(61.8 - 72.7%) -- guaranteed 2HKO
So if you
do manage to get the 2hko, you're gonna be left with a pretty damaged Donphan that struggles to do much else after taking 'Mence out. Just make sure 'Mence is heavily damaged I guess...
Looking at this, the only Ice Shard users are the aforementioned Donphan and
Glalie. I've been liking the look of Mega Glalie in this meta but am yet to try it myself (gave Moody a go, it was fun but so unreliable). It does 63% minimum with Ice Shard so 'Mence can have a little more health and still be revenge killed in one hit. It also has that
huge Explosion which is way more viable here than in 6v6. I mean just look at this:
252 Atk Refrigerate Mega Glalie Explosion vs. 252 HP / 252+ Def Mega Sableye: 162-192
(103.1 - 122.2%) -- guaranteed OHKO
I suck at killing Sableye so maybe this is my answer (please no Protect / Will-o-wisp tho)