Looks more like a type of cereus monstrose. Rainbow cactus are more barrel shaped. As a side note, if that's a fake flower glued to the cactus you might consider removing it ๐
Hi Tyler, these are my Rainbow and Fairy Castle. Like Steph said- yours looks like a Ming Thing- (Cereus forbesii monstrose crest), and Iโd definitely take the fake flower offโฆ๐