Hello!

Source:

https://www.instagram.com/athenapalmer_fg/p/C5bB7jpuJ3k/?img_index=1
https://www.reddit.com/r/BaldursGate3/comments/1bx0r09/wrestler_makes_her_entrance_as_karlach_athena/

The Reddit link was the only place I could find video without 3rd party commentary. Athena Palmer from Ring of Honour (part of AEW) cosplayed as Karlach. From her Instagram:

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A massive thank you to .@larianstudios and @dndwizards for letting me be my favorite character from @baldursgate3 Karlach!!!!

With love and anger

Your #ForeverROHChamp and #DNDNerd

-Athena

Ps.

thank you to @dear.salem for the hair makeup and bodypaint!!!
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So it looks like this was officially endorsed by Larian. Or they at least gave her the thumbs up when she asked. I feel like Karlach would love this.

Not enough horns.

The horns were there. They were in the first instagram picture, and the first 15 seconds seconds of the footage. It looks the pyrotechnics loosened the adhesive the horns were stuck to.