Your partner is recommended to be a Warden as Wardens can pre-emptively put down their Portals on spawn points and actually pull the spawn points to wherever you're stacking
Their gear setup should still incorporate Mora's Whispers and Heartland Conqueror. Their secondary set if doing the round 2 of Arena 1 grind should be Kagrenac's Hope as they will be the last one to live and resurrect you instead of using the resurrection sigil which heals the synergizer prolonging the end of Round 2 (if you're doing a round 2 grind).
This is a build recommended mostly for the normal Blackrose Prison grind experience for XP gain to level your characters' skill lines or to gain more Champion Points.
It's highly recommended you go Altmer/High Elf to min-max on XP gain (especially if you're intent on going for an extraordinary amount of XP) or you can go Nord to save gold/time on your Mythic Ambrosias!
Recommended food will be a bi-stat Health and Magicka food.
Recommended Mundus will be The Lover.
Classes can be Dragonknight, Warden or Nightblade (this is preference but Nightblades and Dragonknights have strong AOE with good healing capabilities while Warden may help stacking mobs much faster).