Short command /summon will spawn all mobs and items in minecraft, moreower this magic command allow to create mob on mob riders! For example - baby zombie on chicken (Chicken Jockey), or skeleton riding a spider (Spider Jockey), and finaly skeletons riding skeleton horses (Skeleton Trap).
What if we need more? More combinations = more fun in game.
This generator allow you create almost any combinations with most popular mobs in minecraft
You may generate more than 2 riders (up to 9). Just push on mob's icons and paste code in minecraft chat. Enjoy!