Loved using Mamoswine from Gen IV onwards. The set I used most often was Sub + 3 attacks: come in to revenge or on a sure Electric attack, and Sub on the switch. Mamo scares a lot of things away with its STABs and power, so this isn't too tricky. Sub on a Swine catches a lot of people off guard, and gives you breathing space to hit something hard.
For instance, a dragon like Dragonite or Chomp KOs something. You bring in Mamoswine, for the obvious Ice Shard. They switch to Keldeo or something, you Sub. Keldeo either switches or breaks your sub and gets an EQ in the face.
Rotom-W is a big problem, so kill that asshole first. Use Freeze-Dry as your third attack (Ice Shard and EQ are non-negotiable), and lure it in. Sub as it comes in, Freeze-Dry as it attacks. Free hit, and you prevent any Trick nonsense too.
And Icicle Spear ftw: such a fun move. Bust enemy Subs and maim what's behind - stuff like Gliscor, which sometimes stays in to get you with Knock Off or Toxic as you break the sub. If you roll 4 or 5 hits, it's dead in one go. Back in the day, Icicle Spear also provided a backstop against FEAR shenanigans from that asshole lv.2 Probopass. I hated that thing.
Icicle Crash is more reliably powerful, but Spear doesn't miss. Mamo is a great 'utility check', with multi-hit, priority, high power and now Freeze Dry to mess with more things than ever.
Mamoswine @ Leftovers
Ability: Thick Fat
EVs: 4 Def / 252 Atk / 252 Spe
Jolly Nature
- Ice Shard
- Icicle Spear
- Substitute
- Earthquake
or
Mamoswine @ Leftovers
Ability: Thick Fat
EVs: 4 SpA / 252 Atk / 252 Spe
Naive Nature
- Ice Shard
- Freeze-Dry
- Substitute
- Earthquake
Not sure about EVs on the Freeze-Dry set - might need more SpA. I like full speed on Mamo to catch things out with Sub or a KO when they don't expect it.