I do some calcs:
Detailed Result:
252 SpAtk Life Orb Starmie Ice Beam vs 252 HP/252 SpDef Trevenant: 46.35% - 54.69%
Possible HP Damage: 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 200, 202, 204, 206, 208, 210
2-3 hits to KO (with Leftovers)
252 SpAtk Expert Belt Starmie Ice Beam vs 252...