How to make dragons

Can someone tell me how to make a minecraft dragon that will have a different texture than the regular dragon and different spawn egg. The only part im struggling with is the model and actually making a mod that does this. I do not want to make a texture pack.

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If you make a mod that has regular enderdragon textures and no spawn egg but with the movement and everything like the regular dragon, I will appreciate it a lot. I just need help with the movement and the model of it. Thanks so so much