Couple of suggestions:
- if 1 copy of Opportunity knocks takes 10 weight, then studying 5 copies of it should cost 50 for example.
- If Opportunity Knocks is only given by stronger animals, then it should take more mental weight then lets say Punch.
- If Studying 2x copy of Opportunity knocks takes 12 hours, then studying 4x should take 24.
Reasoning:
I do not like the idea of a combat alt being able to study up 5 copies of all of the best skills needed for combat. I think they should have to put some effort into their character. I think study time should be increased and so should mental weight.