What is wrong with those stats?...besides the physical ones are all above 100
Aside from Speed that probably could be better but good enough for Garchomp (...whatever it might do besides use Dazzling Gleam or lay hazards in a lead vs lead scenario) the stats are actually pretty good and the paper Defense honestly isn't anything new in the magical realm of fast but frail attackers. See: Weavile, Alakazam, and Breloom. It's kind of like Bizarro Diancie if it were allowed to have better Special Attack and Speed without the need to mega evolve.
That said, I don't see this thing succeeding highly in old gen terms since it has some awkward defensive typing that's weak to common types (Water's water, Steel's gaining now that # of Fairies are increasing, Psychic is kind of so so but threatening nontheless, and everyone and their mom carries Earthquake). It's too bad it can't deal effectively with Steels either without using HP Fire, and even then it has a mostly terrible matchup against Heatran variants with Earth Power. So I'm thinking:
Nihilego @ Life Orb
Ability: Beast Boost
EVs: 4 Def / 252 SpA / 252 Spe or 80 Def / 176 SpA / 252 Spe
nature: Timid
- Power Gem
- Sludge Wave / Sludge Bomb
- Hidden Power Fire / Thunderbolt
- Stealth Rock / Toxic Spikes / Grass Knot / Thunderbolt
Basically your average offensive Rock setter/attacker, though it performs terribly 1v1 against a majority of ORAS leads so it's more advised as a first-to-second quarter (1/4 - 2/4 of the battle) setter. If you don't wanna deal with that shit, then go for a fourth attack.
80 Def / 176 HP / 252 Spe with a Timid nature makes Nihilego's Special Attack lower than its Speed, giving it a Speed boost instead of an SpA boost when Beast Boost activates while still outrunning Garchomp (even w/ imperfect IV). Even with wackass coverage, that's pretty big against fast offensive teams. If you wanna break through stally/bulkier teams with SpA boosts though feel free to max SpA out or go big with Modest.