I'm sorry to pick at this vigorously, but not only is this not a core, but these sets are not even well constructed or competitive.
A defensive core consists of partners who can switch in and out of offensive threats. This core fails to do that because they not only share the same weaknesses, but share the same offensive threats with no real way to scathe them.
Fairies severely lack solid physical defenses, so CM/Cleric/Support Sylveon should always run a physically defensive orientated or mixed spread. Furthermore, not only does Draining Kiss make disuse of one of the best offensive abilities in the game, but it now gives Sylveon a useless ability and helps it assert itself as a passive mon. Also, Clefable > non-Pixeliate Sylveon.
I've seen Sub-Seed Whsiscott put in some work in this tier. I've used it with success on low/mid ladder alts for giggles. Under the right circumstances and with the right set, Sub-Seed Whimsiscott can be incredibly effective. This is not that set. While Switcheroo Flame Orb can be great for catching CB Scizor, Landorus-I/T, Skarmory, Exadrill, Ferrothorn and the like off guard, it means that you can only ever switch Whimsiscott after a knock out, as any other means reveals the Flame Orb and instantly cripples the set. Furthermore, you are never certain of what item you'll receive. If you find that you tricked yourself a choice item, then congratulations on acquiring a useless slot.
Bulky Mega-Gardevoir is a neat set, but I don't believe it to be one that should ever be used on a Fairy team due to the structure of the type. The best way to utilize this build would be with a Wish passing set. Generally, Clefable would be the better user of this set, but Gardevoir can become a niche user due to Will-o-Wisp, a great speed tier, and an immediate offensive presence. Consecutively, Confuse Ray is not only uncompetitive due to its unreliability, but it does nothing for this set. Sure, it can force a switch and allow you to set up a Calm Mind, but Mega-Gardevoir already forces switches and finds ample opportunity to set one up.
Here is a revised version of this "core." I'll actually come back to this later and optimize the EVs on Togekiss and possibly Sylveon.
Sylveon @ Leftovers
Ability: Pixilate
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Wish
- Protect
- Heal Bell
- Hyper Voice

Azumarill @ Choice Band
Ability: Huge Power
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Play Rough
- Waterfall
- Superpower
- Aqua Jet
Togekiss @ Leftovers
Ability: Serene Grace
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Wish / Thunder Wave / Air Slash
- Roost
- Defog
- Flamethrower
The core is simple. Sylveon and Togekiss keep Azumarill alive long enough to put dents in teams. Choice Band because that actually allows Azumarill to break through just about every threat bar Mega-Venusaur. Skarmory, Ferrothorn, Scizor, Bisharp, Excadrill, Victini, Jirachi, Hoopa, etc are all 1/2HKOd. Heal Bell allows Azumarill to play agressively versus Wisp users and Scald spanmers, all the while ridding Toxic from itself and Togekiss. Togekiss prevents the core from being worn down by hazards and acts as an emergency check to the likes of Scizor and Bisharp.