The Jokelocke challenge is not an ingame challenge, but rather a set of self imposed conditions based on the nuzlocke challenge from pokemon.
Base rules:
a1) Selling or destroying a joker kills it, you cannot buy or otherwise obtain a copy of it later after you lose it. (Clarification: a) for this purpose and other rules Riff raff, Judgement, Soul and other joker generators that don't let you control which joker you get are banned. b) Some exceptions are made)
a2) You can only obtain one joker per round, this joker must be one of the first jokers you see, rerolls are allowed only if no jokers appear in the shop. (Clarification: a) While gaining more than one joker per round is not allowed, I do consider the corner case of finding, say, a polychrome Riff raff that you want to take. Particular cases like this are allowed as long as the joker generation effect never activates, under this clause you can also keep a judgement for tarot blocking as long as you don't use it)
a3) Rounds may not be skipped. (Clarification: a) "You can't run from a trainer battle")
a4) Hand levels are capped at the current ante number + 1. (Clarification: a) Ante 2 means your max hand level is 2, you may upgrade a hand beyond the limit but may not play that hand until you have the proper max level. b) Going back an ante through the use of -1 ante should be considered as lowering the max hand level, although you can probably skip this addendum if its too annoying) c) The Wall, Violet Vessel and any other blind that increases the neccesary scoring beyond the usual instead grants a +4 to the hand level limit