She's the final reward from Seige, which begins this month.
From Plarium:
Authoratix Lamasu is a great Champion for both PvE and PvP content.
Having Decrease ATK debuff as a part of her A1 and being able to place Block Buffs along with Decrease SPD debuff on her A2 with no hit when targeting a Boss (which means the debuffs will go through Poison Cloud) makes Lamasu a valuable addition to your Hydra team.
Add a True Fear debuff to control the enemies, a single target A3 skill to support an ally by removing all debuffs and placing Intercept to protect them from control debuffs (Sheep included 🐑) and the ability to boost the Turn Meter and reset the CD for that very same ally in addition to a unique Passive skill providing Authoratix Lamasu the immunity to Sheep debuff and now you have a perfect match for Arena battles.
Sprinkle that with the ability to destroy enemies' ACC and RES, and you'll get an overall amazing Support Champion that can help your team in long fights and will be a great new addition to your roster.
I hope she can be obtained the same way Mithrala is won...i.e. depending on your own efforts and not on the efforts of a whole clan.
If it is the later, only the whales to krakens will ever get her
I seriously doubt she's going to be unobtainable for everyone. Of course it'll take longer for some than others but with these types of champs they've always been available to all players.