Pikuniku

Really easy to get on coop level 3. Got it on my first attempt when I was still exploring the level a bit, with a time of 2 minutes 36 seconds. (while controlling both controllers by myself)

At the start, hold on both controllers to go all the way to the left, until you reach a trapdoor which needs to be opened by kicking the buttons on both sides simultaneously. Afterwards, drop down and get both of you characters in a car. For most of the remainder of the level, you will be holding the stick to your right to drive the cars. If one car lands topside down (and you cant move further), get out, flip the car with and get back in. Keep your attention on the arrows as well. At some point, you will have to go down left, in order to progress. Once you reach the end of the race and crash in the water, get out of the car and swim to the right. There is a boat here. If both of your guys sit on the both in their spot (while holding ), the level will end.

There is no online co-op, so you will need two controllers. Every co-op level is unlocked automatically. If you don't have a friend to play with you can easily do this by yourself. Co-op level three is a race, you need to do a small amount of platforming with both Piku and Niku and then each of them gets their own car and you just need to hold to the right and then left and then back right (following the arrows) until you get to the end of the level. You can redo these levels as much as you need to.