Well everyone has gone and done the more viable support sets, let's go with gimmicks! Nope, not Swagplay. Item switch.
[email protected] Orb/Flame Orb
EVs: 252HP and 252 Def/4 SDef or 4 Def/ 252 SDef
Nature: Bold or Calm
Substitute / Protect
Toxic / Thunder Wave / Spikes
Switcheroo and Prankster switches out their item real fast. Klefki is also faster than Sableye, so this is great for crippling it before it can taunt. Other tanks and walls also don't appreciate being given a status item. Substitute/Protect scouts the enemy move and give you more turns of tick damage. Foul Play is for attacking if ever Klefki eats a taunt. The last move is for further support after the item swap: Toxic for more damage, great with Protect. Thunder Wave is for extra annoyance. With Spikes, Klefki might get a free turn to do it, because of possible switches caused by Toxic Orb/Flame Orb.
Toxic Orb is easier to manage than Flame Orb, since you don't need to swap immediately as Klefki is immune to poison status. Flame Orb has the benefit of crippling physical attackers that don't have Guts or Facade.
Switcheroo (and Trick) are weaker now because they are blocked by mega evo stones that you can expect one per team, and there's the possibility of getting stuck with an Assault Vest, but don't let it deter you.
Other possible items to swap around include Choice Band/Specs/Scarf and Lagging Tail. Choice items are best for locking supports and tanks into undesirable moves, forcing a switch. Lagging Tail is to cripple non-priority sweepers.