Well... you can practically make a dummy spell for each case, which practically does nothing. And then, you have a trigger like this:
Event - An Unit Starts the effect of an Ability
Conditions - Ability Being Cast equal to Tralala
- Random real between 1 and 100 is lower than or equal to ChangeOfSucces (change ChangeOfSuccess with the percentage chance, number between 1 and 100)
Actions - Create 1 dummy unit for owner of (casting unit) of position of (casting unit)
- Set 1.5 seconds expiration timer to (last created Unit)
- Order (last created Unit) to Human - Mountain King - Storm Bolt (Target Unit of Ability being cast)
The ability which the dummy casts can be adjusted to the ability you want. If you want the damage to always occur have the normal stormbolt do damage and the dummy one do no damage but have it stun the unit. Stun can be adjusted through the duration.
About the targetable spell with % change you need to go the same with dummy units. If you want different chances for each level, then you can just put the second condition through IFS and base on dummy units once again. Its pretty easy if you get how to do the storm bolt stuff.
The last one, I think it already exists. Look at Goblin Tinker's ability and try to get how it was used. I never used that ability so I can't advise you how to use it. Though I could easily try to get it...
~Daelin