Shell Smash + perfect coverage
Barbaracle
Tough Claws
Adamant/Jolly
Expert belt*, Shell bell, Life Orb, White herb
EV's: 4hp, 252atk, 252spd
Shell smash - instantly double your attack and speed
Stone Edge - STAB, higher crit rate, but only 80acc
Earthquake - coverage
X-scissor/Poison Jab - Coverage, wreck grass switch-ins
The choice between X-scissor and Poison jab is tough for a lot of reasons. Edge-quake is resisted by only a few Pokemon (disregarding levitating steel or ground types, which can easily be countered by one or more of your teammates). Breloom, Chesnaught, Virizion, and Torterra all naturally resist Edge-Quake. The first three are weak to poison, but neutral to bug, and the last of the four is neutral to poison. Chesnaught easily takes a +2 X-scissor at 50% health loss per XS, but cannot stomach a poison jab with prior damage from spikes or stealth rock. Breloom, Torterra, and Virizion are ohko'd by either coverage move.
Levitating Pokemon that resist Edge-Quake: Flygon, Lunatone, Solrock, Claydol, and Bronzong. Flygon is neutral to bug, but resists poison and has only a 6.3% chance of being OHKO'd by SE after stealth rock, but it cannot switch in on an X-scissor without getting OHKO'd, regardless of an entry hazard. Solrock, Lunatone, and Claydol are all weak to XS and will get OHKO'd. Sassy Bronzong is immune to poison, but takes neutral damage from XS and loses half of its health from SE, so it isn't a safe switch unless it switches in on earthquake. Physically defensive Bronzong still cannot take 2 XS, but is no longer 2hko'd by Edge-XS. Given that, a fully defensive set will not be able to do much against you and can easily be revenge-killed via pursuit (now neutral against steel, making it supereffective and a guaranteed kill).
That said, gravity support would work wonders for the barnacle in dealing with these potential counters.