The spell descrition states it convinces the animal that you mean no harm. and it fails on INT 4+. So it is especially for beasts like this. And the ability to speak to it should make us able to make clear what we plan to do. The owl bear even realizes that it has something in its eye.
This is exactly there you misstake is.
I repeat:
Owlbear is a Monstrocity ... not a Beast.
Sorry, I realized I was wrong about it being a beast. You're correct there. For whatever reason, I swore it was listed as a beast this round. With all the options, I can see fudging the rules for speak with animals to work on certain monstrosities like this, but limiting the control of it.
Then, by all means, animal friendship should not be castable on it. And also the later befriending of the cub impossible. so we are back to a game specific decision. Pity.
Monstrosities were befriended and tamed/trained in Forgotten Realms. Even if animal friendship doesn't work on it, it still happens in the rest of the lore.
