Unlocking new decks (KM)

[Percussigant]

Is there a way to unlock the alternate starting decks without having to win a run on max challenge difficulty ?

[Chaoz]

Nope, sorry, if you wanna progress, you gotta tough out the challenges. I know some runs can feel like bullcrap, it can be pretty difficult, but stick with the Goat/Triple Blood deck until you find the Mantis God deck, then just use that for everything else. If it helps, try picking challenges that compliment your playstyle so that the drawback doesn't hurt you as much (don't use items much? Reduce the amount you have, etc etc)

Also, if by "max challenge" you mean "do I use all the skulls/challenges", no, you just need to meet the score quota, which doesn't demand every skull's activation.

[Percussigant]

Thanks. So I do not need to win the current challenge level with the latest unlocked deck to unlock the next one ? Winning with any deck works ?

[StayPuftMM]

Correct. The only thing you get from winning with a deck is a checkmark on the deck and there's an achievement for winning once with all decks. You can win with the deck with zero challenges and still get the checkmark.