Ghostly Owns said:
Whooie! What a long post!
1-"How Undyne the Undying can take on Beerus?"
Guy. Just look at her profile
Undyne's profile She has enough Durability to take on him directly and has enough AP to demolish him
2.-Let me read your point
"They don't seem like they can even destroy a planet. So they don't have that AP"
Yeah, Sepphiroth also don't have enough AoE to destroy a planet, for example. But has damage things that could do that and much worse. Get the point? Even if their attacks "Don't look like" they can. They can damage a being with enough durability to endure the destruction of a multiverse. That argument is weak, very weak.
3.-I don't want to be rude (At all) But debate about "What if Beerus was bloodlusted..." is a bit pointless. OP already specified that both are In-Character. And we both know that Beerus would not one-shot him at first glance. And taking in count that a being with much more durability suffered well because of KR, killing waaay less people. I don't even want to imagine how hard it's going to hit Beerus. The real reason (At least for me) of why this is inconclusive is because Beerus (probably) has far better speed. So there is the possibility of him dodging before KR would instantly kill him or a scenario where he attacks first. Nothing more.