Hey! you're a much better artist than me so take my critique with a grain of salt, your discernment is probably much better than mine, but I think you hadn't exaggerated the square forms on the buffalo and the hippo enough. For an example, you made the ears of the square water buffalo much more pointy than they needed to be, the same goes for the chin and the horns of it as well. While It doesn't look aggressive, it also doesn't have the square sort of structured archetype feel that Matthew Mattesi described. Perhaps giving it a wider jaw and more broad features could help give off that large and strong feel rather than the slender and elegant or majestic sort of feeling it has. The opposite goes for the squared off hippo. I think you had made him too rounded, while he isn't as circle based as the circle baby hippo, the square one still has a very childish or friendly sort of feeling to it, because it's so round and soft feeling. they all look fantastic though