It doesn't really matter lions or tigers but as far as animals go, there are no hostile animals. we could even add bears... the more the better. Is there any other info you need? Cuz all I can think of is the idea of what should be added. I think tigers or lions should run the fastest so it makes it hard to get away from them, this will be what makes them a threat. as far as hearts go, I'd say they shoulnd't be any more stronger than a skeloton or spider. But this would at least add to the atmosphere. If there is any more info you need just ask me.
Also, I've seen mojang writing that they prefer having freindly animals and non-realistic bad-guys or something like that.
If there is any more info you need just ask me.
We don't need to ask you, you need to write it down in the post!
http://www.minecraftforum.net/topic/214909-cats-lions-and-domestics/