I get exactly the same damage for both calcs using http://pokemonshowdown.com/damagecalc/ (Honkalculator 4k), which is as it should be.Edit: Hmm. This is weird, according to Honko Snow Cloak Mamo is KO'd by Jolly Chomp while Thick Fat isn't (notice I'm not using sash). But Thick Fat should reduce only Fire and Ice damage, not water damage. This is weird.
+2 252 Atk Water Gem Garchomp Aqua Jet vs. 0 HP / 4 Def Mamoswine: 314-370 (86.98 - 102.49%) -- 93.75% chance to OHKO after Stealth Rock
Out of the things that Haxorus gets, the only thing that it really enjoys is Close Combat; with Dragon/Fighting coverage, it doesn't really need anything beyond that and would prefer setup moves or one setup move and Taunt. The problem with Aqua Jet is the same as with Garchomp, except it isn't walled by more things; it has 4MSS when considering that the 5th move is a weak non-STAB move that really only has a very niche use. If it chooses to forgo Dragon Dance and use Swords Dance instead, it immediately becomes vulnerable to a lot of faster mons (Lati@s, Starmie, other Dragon-types, Rachi, etc), but if it chooses to use Dragon Dance, it needs twice as many boosts to beat Mamoswine. Overall, I don't really think that Aqua Jet will be all that useful for Chomp and Haxorus, but it does have a niche.
Some other things no one has mentioned:
- thanks to Miltank, Snorlax finally gets reliable recovery, so it need not rely on Rest anymore. The same goes for Piloswine, but whether it is at all viable is another question entirely. It does mean we get Ice Shard Snorlax though :>
- Also, Shift Gear Metagross! I suspect it could be quite scary, since it has fairly good 3 move coverage, and is fast and strong when it has a Shift Gear boost under its belt. Klinklang also gets some coverage moves, but it's likely overshadowed by Metagross.
- Swellow finally gets a movepool that allows it to beat Rock-types; Close Combat and Earthquake are both available from Heracross.
- Sigilyph gets Quiver Dance with two of its abilities, but neither of them are Magic Guard, which is part of what makes it so fearsome, so that's a bit disappointing. It also gets Baton Pass when it uses Wonder Skin (Venomoth), so I guess it could QD pass if it uses that.
- Conkeldurr and Golurk can both get Roost and Slack Off from Ledian and Infernape respectively. Golurk can also use STAB Shadow Claw from Infernape, but it's still weaker than Iron Fist-boosted Shadow Punch.
- All Swift Swimmers get Baton Pass, Shell Smash (both Gorebyss), Rapid Spin (Kabutops), Dragon Dance (Kingdra), Leech Seed (Ludicolo), (Toxic) Spikes (Qwilfish), Icicle Crash (Beartic), Encore (Golduck), Swords Dance (Kabutops), Superpower (Kabutops/Beartic), and Head Smash (Relicanth). Between those there are some potential threats I suspect. There are probably other moves that I have missed, but I think that's most of the relevant SwSw ones.
- Head Smash/Swords Dance Rock Head Aerodactyl (Aggron and Marowak)