Here you can make a list of your custom challenges so that others can read this thread and try to complete those challenges which can make the game more fun and inventive.Here are mine(will update regularly):
1)Complete the game without any magic.You can use blink only in that Void mission where you learn blink.
2)Complete the game with low chaos using your sword to kill at least three times each mission.
3)Finish the game without taking damage.
4)Complete the game using only blink and sword.No gadgets allowed.Sokolov's health elixir and Piero's spiritual remedy is not allowed to be used even once.
5)Assassinate High Overseer Campbell with a pistol without alerting anyone.
6)Kill the Pendelton Brothers by drowning them.They must not die before drowning.
7)Frame Curnow for Campbell's death but protect him and his guards without killing or alerting anyone.
8)Kidnap Sokolov without rendering him unconscious(Don't know if it works)
9)Kill lady boyle from a distance of at least 150 metres.
10)Kill 3 tallboys with a springrazor on each.