Everyone is too busy discussing the MLP side of things, but nobody is mentioning the Transformers.
They dealt with mind control before, and they are an X factor that Sombra can't plan for, because he's not used to fighting them.
Like, I'd like to hear your opinions on the chances Optimus Prime, Megatron, Soundwave, Shockwave, Arcee, Bumblebee and the rest have of fighting off King Sombra.