What type of goldfish or any other small fish are compatible with the comet goldfish no fighting?

Almost all goldfish can get along! i would recommend a ryukin, black moor, ranchu, fan tail if your looking for a goldfish, but for other lil critters, maybe a freshwater snail, or minnows (you can find those at a local creek) or a freshwater frog, Just make sure you have a lid and a place for the frog to take a break and hop out of the water. Comet goldfish are very fast and somewhat aggressive. Fancy goldfish should not be housed with comets because fancy goldfish's unique features/bodies often prevent them from being able to compete for food. A good tank mate other than another comet would be a shubunkin or a wakin because these fish are built similarly to the comet and can compete for food. As for a community- goldfish really should only be housed with other goldfish.