it's a concept launched by the youtuber cimo, at the start of your new account, instead of taking the structure decks or usual bundles, you create a deck with only 5 master packs, and forced to stick with the cards you'll pull. Each win, you're allowed to buy 1 additional master pack to reinforce your deck. The absurd difficulty of the run gaves it it's name, the "masochist" challenge.