Right so things that currently threaten this core include fast dragons, ground types (especially Excadrill), and to an extent, steels (Ampharos has to rely on Focus Blast, while Gengar can only passively wear them down. So anyways, might as well go with something that can handle most of these threats.
Mamoswine @ Life Orb
Trait: Thick Fat
252 Atk / 4 def / 252 spe
Jolly Nature (+Spe, - SAtk)
- Earthquake
- Icicle Crash
- Ice Shard
- Knock Off
So I picked Mamoswine because he handles many of the threats that can crap on what we have so far. He takes care of any grounds through the use of Icicle Crash, and Ice Shard. Slower Steels that don't rely on Steel STAB (think defensive Heatran (who forces Amphy to rely on a shaky Focus Blast while doing barely anything with his other moves)) can be handled by Earthquake. This set is also able to check many of the dragons and flying types in OU, sporting the most powerful Ice Shard in the game. If prior damage has been taken, not even a Weakness Policy Dragon Danced Dragonite can stand a chance thanks to Extreme Speed not OHKOin while OHKOing in return with Ice Shard. This also applies to things like Lando - I, Garchomp, and to an extent, Lando - T (Intimidate is a bitch though). The last move goes to Knock Off, as Mamoswine gets enough coverage already with Ground/Ice STAB, and is also able to force switches thanks to his great offensive presence and removes items in the process.
Mamoswine also works well with Gengar and Amphy, as Gengar can come in on a fighting or grass type move aimed at Mamo, while the grass, water, and steel weaknesses (mainly Scizor and Excadrill) are covered by Ampharos. Mamoswine can come in on an ice move aimed at Amphy thanks to Thick Fat, as he gains a pseudo resist.
If we go down this route, then something that can handle Excadrill is sort of a must.