Saving SC2

Terran
Stim has 5% chance of killing the marine but also a 20% chance to give it 30% extra attack speed and movement speed.

Yamato cannon has a 20% chance to split into 2 cannons, , which also have a 20% chance to split into 2 more cannons, targeting random enemies. They cost 10 more mana

Salvaging bunkers returns 70% - 100% of it's cost

Raven missiles have a 15% chance to dud or hit an ally unit but deals a larger area of splash damage

Mules last for 40-80 seconds

Nuke has a larger radiation AoE, up to 30 radius, that deals no damage but gives bio units within the range a 50% chance to have a random (positive or negative) buff.

Protoss
Warpgate warp in has 10% chance of killing the unit outright because of psionic interference - and a 10% chance to warp an additional random gateway unit of any tech.

Colossi have a 10% chance to get stuck between the cliffs*

Psi storm does 5-30 dps

Chrono boost costs 10 more mana but has a 5% chance to instantly complete the production of a building

The Cybernetics core has a new upgrade for Sentries, which when upgraded gives sentries a choice to cast a normal FF or a "Rocking FF" that cost 100 mana but gives it a 50% chance to spawn Rocking Destructible Rocks instead of forcefields.
These Rocking Destructible Rocks are share the same characteristics as normal destructible rocks and have the same effect when destroyed (as stated in "Misc" below), except that they are skinnable.
Players have to press the first hotkey for forcefield and the second hotkey to decide if it's a normal FF or the Rocking FF.**

After blink is researched, stalkers have a 30% chance to shoot an additional pair of laser beams when attacking, which will hit a random target nearby. When blinking they have a 10% chance to blink in the opposite direction.

*They are already imba so there's no need to balance that with a buff
**Has a 10% chance to spawn as Rocking Destructible Debris.


Zerg
Zergling cocoons have a 2% chance to spawn into an ultralisk but they cost 5 more minerals

Banelings have a 10% chance to detonate suddenly, damaging everything around it. It's movespeed is buffed by 20% in order to catch up with the speed buffed marines

Larva inject spawns 2-6 larvae

Cancelling a a morphing lurker/baneling/overseer/broodlord cocoon has a 16% chance to immediately turn into a Mutalisk The resources spent are returned, and the supply count will increase by 1. The Mutalisk will also gain certain upgrades that the unit had before being transformed. If it doesn't morph into a Mutalisk you will only get 75% of your resources back.

Misc
There definitely needs to be some collectible skins. You get skins by getting achievements or winning tournaments or reaching a certain rank and you can trade it or win skins from your opponent.

When destructible rocks are destroyed random sized fragments are randomly scattered within an area the size of a nuke. The rock fragments damage units that are within the area in relation to the size.

Changelog 1.04: added effect for stalker and nuke
Changelog 1.03: added upgrade for forcefield
Changelog 1.02: added destructible rock feature
Changelog 1.01: added muta lottery for zerg

Acknowledgements: Deathstar, OtherWorld. bisudagger, 29 fps, antisocialmunky, FFW_Rude, Big J