Instructions
Access the "Pokemon" menu and place Sneasel at the top of your Pokemon team. This will make Sneasel your default Pokemon in battle.
Press the "Start" button to access your item menu and equip a Razor Claw to Sneasel.
Wait until night time according to your in-game clock. Night time lasts from 8 p.m. until 3:59 a.m.
Engage in Pokemon battles by either walking in tall grass or walking in front of a rival Pokemon trainer, who will automatically challenge you.
Use your Sneasel to win Pokemon battles until he gains a level. Sneasel will automatically evolve into Weavile as long as it is still night time and he has the Razor Claw equipped.