Tip is not included in the buffet prices. The consensus on this board is that the standard 18% tip is recommended. But I suppose anywhere between 15% and 20% would be good. Tip according to the service. If it's awesome - go high, just ok go with the lower end. If it's awful please tell the manager!
Chef Mickey's is great fun!! We go every year and we have never had a bad server. They are usually very attentive and swift with the refills.
Have fun.