Big fan of this pokémon, so here's my RSE version
Lapras - Calm Nature - Shell Armour
Item - Lum Berry
Moves - Blizzard, Hydro Pump, Rest, Psychic
Strategy - First off, Lapras is brilliant in the sense that it knows how to take a hit.Additionally, it knows how to give 'em back too. Lapras is very, very good with Blizzard, and should you come against Steel types, Hydro Pump isn't too shabby. High HP means Lapras will be around for a good while, and it has mediocre speed. Resting with a Lum Berry sort of gives you 50% to 80% extra hp, provided you don't die before you can use it efficiently. So overall, a brilliant combination of endurance and power gives Lapras an edge over most pokémon.