For completionist Cape, maybe make it work as an ava.. also add the "emote" from the infernal max cape to the comp cape^
Mastery capes being sold at wise old man is a yes from me^ but maybe only for actual skills and not combat.
2b xp does seem a little steep seeing as a lot of the skills are unbalanced.. maybe 200m xp for mastery?
Last thing: if the infernal eel is to stay In game, please add an option to unbind it from a Cape...