Clefairy, in addition to Clefable and Togekiss, is another great option. Although its Speed can be questioned, Follow Me has +5 priority, making it a move that is executed before any other move can be. Now, why I'm recommending Clefairy over its Evolution and Togekiss is because it can take advantage of the Hold Item Eviolite. Also, a major pro to using Clefairy over Clefable is its Hidden Ability, Friend Guard. Friend Guard is an Ability that allows Clefairy to absorb 3/4 of the damage done to your other Pokemon when hit by adjacent hitting moves like the common Earthquake or Rock Slide. I have Clefairy use Follow Me while holding an Eviolite to help my other Pokemon set up while absorbing many hits with invested Defensive stats, the Eviolite, and Friend Guard. Here is the Clefairy set I currently run:
Clefairy @ Eviolite
Ability: Friend Guard
EVs: 252 HP / 108 Def / 28 SpA / 116 SpD / 4 Spe
Bold Nature
IVs: 0 Atk
- Follow Me
- Aromatherapy/Calm Mind
- Moonlight
- Dazzling Gleam/Thunderbolt/Hidden Power Fighting/any move that covers the Pokemon Clefairy is intended to support
While Clefairy is bulky and can take quite a few hits, it can only handle so much. Make sure you don't get cornered, so use Moonlight for viable recovery, Aromatherapy to get rid of that nasty Toxic/Toxic Spikes/Will-O-Wisp/etc., and the rest is up to you. Sorry if this answer was lengthy, but I hope it helps you!