How about this:
Hydralisks get cliff climbing as an upgrade and take some time to climb each cliff.
Since they aren't great against light units, take a while to get the upgrade and are slow to climb they wont be the best for raiding but they will still be a usefull threat. This would also help thier anti-air role since they can climb cliffs that air units could otherwise hide behind. The slow climb could also present micro opportunities, especially against the other cliff climbers which climb cliffs fast.






