To do this you need to get 3 stars in every challenge, some can be quite hard to do in the time so you'll need to be going as fast as you can. This solution will be a guide on how I did them and the time the solution got me. To get 3 stars you will need to be under the time provided with each challenge.
1.
Destroy 7 vehicles
3 stars - 9 seconds
When the timer starts point your right stick to the bottom left, when the timer is up you'll start shooting, when the vehicle is destroyed move to the next one which is directly left of you, keep going clockwise around until you destroy all of them.
My time - 7.56 seconds
2.
Destroy 4 tanks
3 stars 11 seconds
When the timer ends, go to the one in the bottom left and shoot it until it gets destroyed but don't stop shooting as the next tank is right above it, while shooting that tank move towards it and it will get destroyed when you reach it. While still shooting aim towards the tank to the right of you and moves towards it, when you reach it's position and it's destroyed, start shooting the next one until it's destroyed.
My time - 8.63 seconds
3.
Move 2 vehicles
3 stars - 4 seconds
As soon as you start move to the vehicle in the top left and in a fluid motion hold A and pick it up along with the other vehicle, you will now be holding both vehicles so without stopping go over to the drop zone in the bottom right and press A to release one vehicle and without stooping release the other in the drop zone above.
My time - 3.13
4.
Move 4 generators
3 stars - 9 seconds
When you start go to the generator right in front of you and press A to pick it up and then go to the socket on the left and press A to place it, now following the anti-clockwise route go to the next generator and place it in the socket closest to it, keep going around the base until you've placed all generators in their nearest socket without stopping.
My time - 4.39 seconds
5.
Capture 1 base
3 stars - 12 seconds
When you start go to the troops on the left and hold A to pick them all up, once they are all aboard your Mech fly over to the left base entrance and press A two times to release two of the troops, while they are going into the base go to the top entrance an place the last two troops when all troops enter the base it will be captured and the challenge is complete. The reason for doing this is when you place all four at one entrance they will usually clump up and take a long time to go in.
My time - 10.03 seconds
6.
6 Upkeep
3 stars - 20 seconds
Press up on the D-pad to create troops, you can only have 5 things in your build queue at a time so once the troops have been built hold A to pick a few and press up on the D-pad again. You don't need to place the troops in the pads surrounding the base so go to the right and press A until all troops are offloaded, go back to pick the last of the troops and place these down to the side as well.
My time - 6.63 seconds
7.
Capture 1 base
3 stars - 18 seconds
Go over to the enemy base change to your Mech form and start shooting the base while doing this press up on the D-pad four times to create troops, once all of the troops on the enemy base are destroyed transform back to flight mode, go over to your base and collect your troops by holding A. Make your way back to the enemy base and place two troops at two different entrances preferably the ones closest to you, once they enter the base the challenge is complete.
My time - 16.33 seconds
8.
Destroy 12 enemy vehicles
3 stars - 60 seconds
When you start head over the to the turrets to the right and hold A to pick them up, place these closer to your base so they can destroy the incoming vehicles ( I placed them near the sockets). While they are destroying the vehicles, build 5 Gatty's and place in at the wooden entrance where the enemies come from until it's blocked and the tanks can't get through these will now start shooting at the tanks, now turn into you Mech and shoot them until they are all destroyed.
My time - 36.46 seconds
9.
Destroy 36 enemy vehicles
3 stars - 45 seconds
Once you start change to Mech form and go into the pit to the left to destroy the 4 vehicles, now go back up to destroy the enemies coming from the right go clockwise round the map destroying all enemies until you reach the stone bridge at the bottom, go over the bridge and destroy all enemies coming towards you, these enemies and the enemies your troops at the base have destroy will complete the challenge.
My time - 24.56 seconds
10.
Capture 2 bases
28 seconds
Pick up the the Gatty to the right of the base as soon as you start and place it on the bridge to the right of their base, this will kill all of their soldiers coming in from there now change to your Mech and start attacking the enemy base when the soldiers on their base are killed, your troops will have already captured the other base, just build another soldier to make four and place him at an entrance of the now neutral base.
My time - 23.99 seconds
11.
Capture 5 bases
3 stars - 60 seconds
Pick up you soldiers from the pit in front of you and capture the base, now build 4 soldiers and capture the neutral base on the left of the map, build another 4 soldiers and capture the neutral base on the right of the map. Now destroy all soldiers on the enemy base on the left, create 4 soldiers of your own and capture it. Finally, ignore the tanks get rid of the enemy soldiers on the base on the right, create another 4 soldiers and capture it by going round the back of it to ensure the tanks don't kill your soldiers.
My time - 46.33
12.
Destroy 18 enemy vehicles
3 stars - 120 seconds
Start by destroying the vehicles to the left and make your way round the map in a clockwise fashion destroying all vehicles along the way not forgetting to destroy the tank on the wooden tower, you will finish at enemy base but will not have kill the soldiers in it. All vehicle will be easy to destroy and you will level up while destroy them so there will be no reason to re-energize at a base, there is also no point in capturing the neutral base on left.
My time - 20.63 seconds
13, 14 and 15
Win the game
3 stars - 10 minutes
When the game starts sell all the generators attached to your fortress and replace them with Moneymakers, when that's done start building longhorns and sending them to capture bases and your fortress will make soldiers on it's own which will go to capture the bases but you can build soldiers on your own to speed the process, you an also assist the longhorns by killing the troops on the bases, while doing this you will level up, buy whatever abilities preferably the Guns ability and the guardian ability to give you extra fire power and damage. Once all bases are captured send all longhorns to attack the enemy fortress, start shooting at the fortress as well and keep going back to the nearest base the re-energize and if you want you can build more longhorns to attack their fortress. This method should work for all three challenges but if you are having trouble with any of them tell me in the comments below and I will make a solution for each of them.
My time:
13 - 4 minutes 22 seconds
14 - 5 minutes 10 seconds
15 - 8 minutes 23 seconds
I hope this helped you get this achievement, if you had any trouble with any of the challenges please tell me in the comments and I will try help the best I can.