In my opinion, I think the armadillo is a good addition because it would best connect to the central game. This is because wolf armor would be useful and would theoretically be used pretty often. In a way, I think getting wolf armor will be sort of like a "Main Quest" instead of being a "Side Quest" like other mobs. Also, wolf armor seems to have some good potential, the best example being if the armor is customizable.
For the crab, I don't really favor the idea of the crab claw. I'm not sure if it's just me, but the crab claw doesn't feel like a fitting item for Minecraft (it has Terraria vibes :P). Also, the crab only spawns in Mangrove Swamps, which is a biome I've never seen in-game once honestly. I know that the crab claw is intended to be in a rare biome so that it's harder to obtain and that it would give players a better reason to visit a Mangrove Swamp biome, but the crab claw isn't that appealing to me. I see how it would be useful though. Also, the Mangrove Swamp seems like a slightly odd place for crabs, even if some do live there in real life.
For the penguin, I like the idea of there being more life to cold oceans and stony shores. However, the faster boat concept isn't as interesting to me.
Anyway, here are my rankings:
- Armadillo
- Penguin
- Crab
I'm most likely voting for the armadillo, but I wouldn't mind if the penguin won.