06-01-2016, 04:43 AM
Adding more animals (such as a turtle) is not possible with the current API without a large amount of hackish code (similar to things like the Spigot plugin Slimefun). You would be limited to doing things similar to command block "mods" which, while mostly possible in the Cuberite API, is inefficient and hard. Cuberite does not and likely will never support adding mobs, blocks, items, etc into the game. Forge is the only well developed platform that allows this.
Pets of the current mobs may be possible. I'm not familiar with mob and AI related parts of the API, so I can't say for certain.
TL;DR: No, just use Forge. It's the best platform to date, and there's plenty of optimizations you can do. It's difficult if not impossible to get it close to the performance of Cuberite, but it actually supports what I believe you want.
Pets of the current mobs may be possible. I'm not familiar with mob and AI related parts of the API, so I can't say for certain.
TL;DR: No, just use Forge. It's the best platform to date, and there's plenty of optimizations you can do. It's difficult if not impossible to get it close to the performance of Cuberite, but it actually supports what I believe you want.