Even a simple LO set is amazingly effective. The speed increase this gen might, ironically be a boon to mamo, as it lets it run Adamant without much worry. Honestly, this thing just rapes stall. Pure special Ferrothorn can be koed with 2 earthquakes. Skarmory is koed by 3 icicle drops. While that may sound bad, Icicle Drop as a 30% flinch chance, meaning that more often than not, you can get 2 Drops in a row without it roosting at least once. Both Jellicent and Swampert are also 2 hit koed by earthquake. Most other walls besides bulky waters take SE damage from Mamoswine.
Against offensive teams, Mamoswine is still useful. Ice Shard easily revenges stuff like Garchomp and Nite with miracle scale broken. Mamo is also never koed by any unboosed move by dory, and can ko with balloon variants with icicle drop+ice shard. He also completely wall head Thundurus, although NP sets have focus blast/hammer arm. If you can predict your opponent's switchin to mamo, you WILL be able to smack it hard.
Sadly, Mamo no longer has the 3rd strongest OU earthquake, he has the 4th. Dory has 5 more attack than him.