The frogs are pretty tough, I don't think you can be prepared enough for their ambush at level 2 or 3, if you don't know it is there. They can attack so often, they instantly can kill even a tanky one as far as I remember. Same goes for the crocodile, if one of those beast suddenly teleport at the not expecting casual gamers. But what can you really screw you up at the beach it the fear. If you can't stun lock them to prevent it, the fears can totally get your team killed.
My friend and I aren't that bad at this game, but on our first run we had quite some issues with those fights, while we were still figuring out the new combat mechanics.
