I used Brukan’s “double a minion’s attack” to permanently double a golden Tarecgosa until it’s attack hit 2.14 billion. Once it hit that number, not only could I not buff it any further (attack OR hp), it straight up would not interact with any minions in combat. It stopped doing damage, and caused enemies deathrattles to bug severely (including a Leroy straight up doing nothing on death)
I can happily provide both screenshots and video recording upon request, although I do not know how to attach them to this post. Thank you!