Brawlout

This is for unlocking every character "variant". Character variants are basically clones. They play similar to other characters and the character models are very similar if not just slightly altered.

This game at launch has six original characters and three guest ones. The guests do not have variants.

Basically pick any of the original characters to play as and in every mode that character will level up towards "mastery" after the match, this will in turn unlock new things like the cosmetic pinatas, skins, titles or most importantly character variants.

The launch original characters and their launch variants:
Olaf Tyson - Oooga Tooga, Acolyte, Dr. Tysonstein
Sephi'ra - Natu'ra, Nightma'ra, Sting'ra
King Apu - Apucalypse, Apunaut, Funkmaster
Chief Feathers - Senator Feathers, Condor X
Paco - Mako, Gancho Poncho
Volt - Vandal, Ripjack

All of the variants above will unlock at mastery 3, 4 and 5 unless the character only has two then they will unlock at 3 and 5. If those characters get another variant added I assume they will be put to unlock at level 4 and should unlock retroactively if you already got to that level or beyond.

If you purchase the Deluxe Edition then you got a DLC that unlocked five character variants already. This means you will have to play some characters less to get this achievement done.
Paco you will not have to play at all, both his variants are unlocked by this DLC.
Volt you only have to play up to level 3.
Sephi'ra and King Apu you will need to play up to level 4 each.
Even with that DLC you'll eventually need to play as every character including the variants to max level so you can unlock all the skins for this achievement:


This achievement requires internet. This is also true of all Xbox One achievements but specifically for this game nothing will unlock while you play offline. You can level up characters no problem but the unlockables tied to levels will not show up until you connect to Xbox Live and this games cloud service. I haven't tested this myself with this version but this is how it worked on PC.

I will update this if they ever change how variants are unlocked or if they add DLC characters/variants via free pacth or paid.