Mawile

Although its base stats are mediocre in every metric, Mawile holds some novelty courtesy of its semi-unique typing. Steel resists Dragon, while Fairy double-resists Dragon, making this poor little Pokemon into a wall against what is generally considered the greatest neutral-coverage type in the game. That said, please don't use Mawile in raids, as even with a super effective Play Rough, its low damage could cost your team the raid unless you've got a lot of support.

Best PvE Offensive Moveset

• Fairy Wind and Play Rough is the way to go for Mawile, as it allows it to fulfill its role as a Fairy Type attacker. Ice Fang can also work, and is optimal when double-effective.

• Iron Head is a decent move, especially post-STAB, but Mawile lacks a Steel Type Fast Move. Pairing it with Fire Fang can work against Ice Types
• Bite, Astonish, Vise Grip, and Power-Up Punch are all worthless for Mawile.

Best PvE Defensive Moveset

• Ice Fang is slightly superior to other options due to its faster damage window, better defensive energy gains, and coverage against Mawile's weakness to Ground attackers . 
• Fire Fang isn't far behind but its coverage isn't as meaningful in many cases. 
• Bite and Astonish have poor damage output and have similar coverage.
• Fairy Wind is good as well, and can keep up with the fangs post-STAB. 
• Iron Head and Play Rough also perform very similarly, but the latter has slightly higher DPS and better coverage.
• Please don’t use Vice Grip or Power-Up Punch.

The September 2019 rebalance gave Mawile a bunch of new options which can let it be flexible depending on the PvP format and Mawile's role. Fire Fang and Ice Fang have identical stats and cover different typings, with Fire Fang more favorable vs Steel-types, and Ice Fang being slightly more favorable against Mawile's weakness to Ground-types, in addition to hard-countering Dragons. Bite is a bit inferior now due to its slightly worse energy gains in comparison, but its typing can still be valuable in certain formats. Fast forward three years and in September 2022 the addition of Fairy Wind finally gives Mawile a STAB Fast Move, in addition to offering much faster energy generation. 

Power-Up Punch is preferred for its low energy cost which lets Mawile bait shields, in addition to its stat-boosting mechanics. Play Rough provides Mawile the invaluable fairy STAB that it needs to perform its main function as a dragon-slayer, while Iron Head charges faster and provides a secondary STAB. Vice Grip is a bad move.