good combo for me on zerg is make lurkers and then make the rest of my units hydra and upgrade them they usually have overwhelmin numbers that take out flyin units and tanks as well, good combo for protoss is cannons at base then make tons of dragoons and upgrade them although they take up alot of room and cost way more than hydras and are a cost unit higher but o well i think a big dragoon hydra fight would be awsome but ive never seen it