Ok, in Temple Siege, Urine does a great job of slowing units down with the firebat's(assault) first spell
It casts disruption web then there's like hallu'd kakarus or something that disappear/appear over the units head and die continuously.
Does this in itself slow down the unit?
Is there something else I'd have to do?

I know follow location and conditions, just need Action(s) help
Thanks

Whenever you move/create a unit over/under another unit, it pauses slightly. If you use this with hyper triggers, and do it constantly, the unit will effectively slow down.

The killed kakaru is what does it, probably. The easiest way is to just constantly move a burrowed unit under the slow unit.

Of course, this only works on ground units, and make sure you move burrowed units to them, rather than creating them on them, since if you create units burrowed they are displaced, only moving them causes them to not be displaced. Many people prefer to use air units, as they won't have problems when the player is near a cliff or other unwalkable terrain.