Setting up rocks or knock off is far from passive though. Compared to most electric counters, Empoleon wants them to stay alive to have infinite chances to get in and ruin the swapped in counter... a counter who likely won't like eating Scald, Knock Off or letting you get rocks in their face. If anything, having your electric type alive is more of a liability since, unless you switch in the pokemon whom Emp already crippled, your team might be 2+ item-less guys.it can fish for Scald burns, but aside from that it's extremely passive.
252 SpA Mega Manectric Overheat vs. 252 HP / 252+ SpD Empoleon: 104-123 (27.9 - 33%) -- 86.3% chance to 4HKO after Leftovers recovery.
Unless I'm mistaken, Latios with Thunderbolt is also becoming popular in ORAS.
0- Atk Empoleon Knock Off (97.5 BP) vs. 4 HP / 0 Def Latios: 134-158 (44.3 - 52.3%) -- 17.2% chance to 2HKO
Not too shabby for an fully minimized negative natured attack.