I bealive that a good core whould be a Togetic with eviolite and Follow me. And for partner a M-absol , M-mawile or Aegishlash because Togetic will take the damage and the other with
two Swords Danse they will get + 4 Attack and with Shandow Sneak or Sucker Punch to KO almost anything with one move
A few things. I don't think that Togetic can take 3 hits in a triple/double battle, which is what this core would function in.
But I suppose you could run a strange max defenses set with Togetic for maximum bulk.
As Komaru stated, Clefable is probably a better option, as it has a better ability, and It can use that Cosmic Power on turns when you feel that your team can take a hit.
But yeah, looking at this, this core wouldn't actually be that bad. It resists each other's weaknesses, and hits hard as hell.
The one thing I would say is that the core is a little physically-oriented, but the more I look at this, the more I like it.
Mawile (Non-Mega) could carry Intimidate, adding a higher chance of survival with Togetic/Clefable, and Mega-Absol could reflect any status moves aimed at it. Of course, you can only pick one, but you know.
The Intimidate thing has now led me to another core I've been thinking of.
Either Gyarados and Mega-Manectric or Lando-T and MegaManectric.
The ManecDos core works well, as Gyarados is immune to MegaNec's weakness, and non-Mega Manectric has Lightningrod, granting in Immunity and a Special Attack boost whenever it's hit by Gyarados' biggest weakness.
Lando-T provides the same thing, with the sacrifice of getting LightningRod boosts, but with the benefit of having a VoltTurn core.
Hell, why not run all three? They don't share any weaknesses, and they offer great defensive and offensive benefits.