Very simple and, will come over time.
Included in various sticker packs are skip star consumables. Just use these in the character select screen or, whilst paused in game by pressing
to skip any challenge that you either dont like the look of or, appears difficult. It will not take long to use 10 of these consumable cards.
Unless you are in a rush, I would only use on the silly difficult challenges like "vanquish 3 players when their health is less than 20"