Stormrise

There's a really easy to get both Stormrise achievements Spray and Pray and Unleashed. It takes less than a minute for both.
Set up a skirmish and make sure you pick a map that you can use any unit. Many maps don't let you use all units.
I set up the energy to high just in case and make SURE you set up yourself to be the Sai.
You have to scroll up to your GT and hit X to switch factions. Hit it until the icon is a triangle pointing up.
Then start the match.
I made a matriarch first, and as soon as she was built I selected her, held down LT and moved the right stick to highlight the Acid Rain ability and it pops right away.
Then I made a Rage, and selected it as soon as it was built and held down LT and moved the right stick to highlight the rage smash ability and then that pops right away.
Watch the video if you need to. It's simple

Spray and Pray

When you hit mission 5 you can spawn a Matriach right away, when you activate the ability by holding LT and using your right analog stick to select Acid rain on the right, you will unlock the achievement. Or if you want it even sooner you can do it at the end of mission 4 when you get like 3 Matriach's and then you can get it.

The Fastest way to get this is by playing a Online match. It is dead so you will need a min of 4 players to get this done!!! The maps that allow 2 players only will void the Matriach's from being chosen, so you will need 4 online. You can also go into a skirmish match and get this.

Select the character after being build and press RT button and click on the Acid Rain Ability

To unlock this achievement you must use the special ability of the Matriarch unit, one of the Sai units. An easy way to do this is to start a multiplayer match as the Sai faction and recruit a Matriarch and then use the Acid Rain ability.