I had exactly the same situation, after copying deck code I saw reveler glowing red like it was banned. Took it out and back in and it was playable. Weird

Updated

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In healadin Equality is second card that was changed. It used to cost 2 mana

https://www.hearthstonetopdecks.com/decks/gift-exchange-tavern-brawl-warlock-2/

AAEBAf0GAA+hBs4GzgfFCeG6AufBAvjQAr3TAoniAv3qAtjuAvH3AtyGA4idA52pAwA=

AAECAa0GBgnQArQD1grL7ALQ/gIMkwShBOUEpAelCcPBAtHBAtLBAtjBAvDPAuuJA+qMAwA=

https://www.hearthstonetopdecks.com/decks/otk-priest-miniature-warfare-tavern-brawl/

Mecha’thun is working well in this brawl because it doesnt require any other cards to combo with

https://www.hearthstonetopdecks.com/decks/mechathun-warlock-void-singularity-tavern-brawl/

I really hope one expansion we will just stop getting Yogg-Saron incarnations.

Now updated for standard version of brawl

I had some fun with OTK Priest, try it out:
http://www.hearthstonetopdecks.com/decks/otk-priest-miniature-warfare-tavern-brawl/

Answer to your first question is positive. There are few highlander warlocks