Aegislash:
252 Atk Life Orb Weavile Knock Off (97.5 BP) vs. 252 HP / 0 Def Aegislash-Shield: 276-328 (85.1 - 101.2%) -- 50% chance to OHKO after Stealth Rock
252 Atk Life Orb Weavile Knock Off (97.5 BP) vs. 0 HP / 0 Def Aegislash-Shield: 276-328 (105.7 - 125.6%) -- guaranteed OHKO
While Weavile has to watch out for King's Shield, it can OHKO even Aegislash with Knock Off, so it must rely on prediction to beat it. One wrong prediction, however, and Weavile dies to Sacred Sword.
COULD WIN, COULD LOSE
Charizard (Mega-X)
Can KO with Ice Punch after Stealth Rock.
Deoxys-D
252 Atk Life Orb Weavile Knock Off (97.5 BP) vs. 252 HP / 4 Def Deoxys-D: 260-307 (85.5 - 100.9%) -- 12.5% chance to OHKO
Weavile prevents Deoxys-D from setting up more than one layer of hazards, and can also OHKO Bisharp with Low Kick.
WIN
Deoxys-S
Weavile wins if Deoxys-S doesn't have Superpower.
Landorus
Ice Punch for the kill.
WIN
Thundurus
252 Atk Life Orb Weavile Ice Shard vs. 4 HP / 0 Def Thundurus: 218-257 (72.6 - 85.6%) -- 81.3% chance to OHKO after Stealth Rock
Weavile wins 81.3% of the time or eats a Thunder Wave. If it knows it won't be that useful for the rest of the match, however, Weavile can just OHKO with Ice Punch.
A+ Rank
Azumarill
no.
Bisharp
Resists Sucker Punch and can KO with Low Kick.
Charizard (Mega-Y)
Can KO with Ice Punch after Stealth Rock.
Clefable
Weavile can 2HKO with Ice Punch, but loses to offensive Clefable.
Excadrill
Excadrill takes 81%-96% from Knock Off, so while it usually wins against Weavile, it will take a huge amount of damage in the process.
Garchomp
One Ice Punch/Ice Shard and Chomp is dead.
Greninja
Greninja usually wins against Weavile thanks to its low weight, but if it KOed something with Dark Pulse or Ice Beam previously, Weavile beats it with Low Kick or Knock Off.
Gyarados (Mega)
Although Jolly Mega Gyarados usually wins if it switches in directly on weavile, this is not the case for Mega Gyarados who don't invest fully in speed.
Keldeo
no. It still dislikes Knock Off.
Mawile (Mega)
no.
Pinsir (Mega)
Ice Shard goes before Quick Attack, so Weavile usually wins.
Scizor (Mega)
lol
Talonflame
Weavile loses against Talonflame, but it should be noted that Ice Shard can force Talonflame to die from recoil damage.
Tyranitar (Mega)
Low Kick ftw.
A Rank
Dragonite
252 Atk Life Orb Weavile Ice Punch vs. 4 HP / 0 Def Multiscale Dragonite: 315-374 (97.2 - 115.4%) -- 81.3% chance to OHKO
Ice Punch can OHKO Dragonite even if Multiscale is active. Also, Ice Shard can remove any Dragonite from play if Stealth Rock is up.
Ferrothorn
Hates Knock Off and Low Kick, nevertheless it wins against Weavile with Gyro Ball.
Gengar
Knock Off OHKOes.
Heatran
Weavile can sometimes take a Lava Plume from a specially defensive Heatran and 2HKO with Low Kick. Offensive Heatran is flat-out OHKOed.
Hippowdon
252 Atk Life Orb Weavile Ice Punch vs. 252 HP / 252+ Def Hippowdon: 198-234 (47.1 - 55.7%) -- 15.6% chance to 2HKO after Leftovers recovery
Things get ugly here. Hippowdon deals a large amount of damage with EQ and usually avoids the 2HKO from Ice Punch. Stealth Rock allows Weavile to beat it, though. Specially defensive Hippo loses.
Kyurem-B
Low Kick OHKOes after Stealth Rock damage.
Landorus-T
-1 252 Atk Life Orb Weavile Ice Punch vs. 252 HP / 0 Def Landorus-T: 437-520 (114.3 - 136.1%) -- guaranteed OHKO
Ice Punch is a clean OHKO even with Intimidate.
Latios
Weak to both its STABs.
Terrakion
Non-Choice Scarf variants lose to Low Kick.
Tyranitar
Weavile OHKOes with Low Kick.
Venusaur (Mega)
Mega Venu actually wins since it has insane bulk and Thick Fat, so Ice Punch doesn't even 2HKO.
A- Rank
Chansey
Weavile can render it useless with Knock Off and then KO with Low Kick.
Latias
Dies to Knock Off.
Mamoswine
Focus Sash Mamoswine wins with Superpower; otherwise, loses to Low Kick.
Manaphy
Weavile usually loses against Manaphy since it can't 2HKO, while Manaphy can either 2HKO back or set up.
Mandibuzz
252 Atk Life Orb Weavile Ice Punch vs. 252 HP / 252+ Def Mandibuzz: 213-252 (50.2 - 59.4%) -- 80.1% chance to 2HKO after Leftovers recovery
Mandibuzz has retarded physical bulk, but Stealth Rock allows Weavile to 2HKO it no problem. Weavile does hate Foul Play.
Rotom-W
Takes a lot of damage from Knock Off, can't KO back with Hydro Pump. It can burn it, though.
Skarmory
no.
Zapdos
KOed by Ice Punch.