Project Spark

Easy solo method to get this is to start each each section with 2 players and at the first opportunity let the second character die and then right before finishing the section press to join back in with the second controller and finish the section.

NOTE: DO NOT PRESS TO JOIN WHILE A CINEMATIC IS PLAYING, THIS GAME IS VERY GLITCHY AND WILL PROBABLY SCREW YOU OVER LIKE IT DID TO ME.

I just used this strategy myself and can confirm it works.
I will note below where to rejoin on each level for anyone that might need it.

1-1
Jump the first islands and then let the first void goblin kill player 2.
Continue with your main character until you are fighting the waves of goblins and join in after the bell tower is destroyed, finish off the remaining goblins and that is 1-1 done.

1-2
Make you way to the observatory with both players this is where player 2 will die.
Play through the rest of the level until you kill 2 berserker golbins AFTER you ride to the top of the observatory, join in here, kill 3rd wave and finish the level.

1-3
You can let player die right at the beginning of this level.
Rejoin after you kill the chieftain but BEFORE you pick up the runestone.

1-4
Again player 2 can die right at the beginning of this level.
Rejoin during the fight with the "Final Spawner" and finish him off

1-5
There is a group of enemies right near where you start to kill your idle player.
Rejoin after killing both Chieftains before picking up the runestone.
As soon as you pick up the runestone the achievement should pop.

Hope this helps anyone having trouble with glitches/bugs screwing them over.
If you down vote please let me know why so i can try make this solution more accommodating.

Local co-op works for this. When choosing your champion, turn on a second controller and hit A to join, and choose a second champion. You will need another person actually playing. You must run through all chapters together, and it will pop after the last one. Chapters do not need to be completed in order.

In co-op, you can also complete the Coup d'état (Karlsnor kills a chieftain), Unstoppable (run Void Storm without dying), and Four of a Kind (all four champions complete without dying) achievements. You only get credit for the character played by the main controller, but it makes runs much easier and faster.