Black Hat's is legit really good. Really thick, dastardly accent with surprising range. Mexican Black Hat is really good too, but the English accent feels right.
Flug is honestly a little better in the Mexican dub. English Flug fits, but not quite as perfectly. Plus he's one of those characters that speaks without a visible mouth, so the VA can say more verbose lines that don't need to fit flaps as long as he says them quickly, and that works with how flustered Flug is as a character.
We've only heard one non-word from Demencia, although it can be assumed the "Rawr" in both versions of that short is from the English VA since it's used in both and doesn't sound like the Mexican VA. Probably will fit well.
Pretty sure 505 is Markiplier in every version, since it's just [scared bear noises].