Mighty Goose (HP)

I was able to beat Krak'Bak (3rd level) in a little over 3 minutes without difficulty. I had beaten the Void King once, giving me a lot of upgrade choices. Personally, I had the Protein Bar and Vark CRT energy upgrades, Commander Vark as my companion, and the Void King Glove as my secondary weapon. However, none of them mattered as much as spamming LT+RT at every available opportunity. Dying resets the entire mission but Krak'Bak is pretty easy once you've run through the game.

There are a couple other levels that are short as well, but Krak'bak worked for me and skips any platforming element other levels have.

Got this on Kolos Prisons without really trying. I would say make sure you use the roll to move around quicker on the early sections and for the boss what I did was spam the bombs with (B) then finish him off with normal shots. Use the booster LT+RT if your tank breaks