Yeah, the game uses different descriptions for it too, Cole mentions 3 skills possible of which 2 already used.
the 3 are taboo, rule (geas) and vow (promise)... Seems Charlie needs to mark a person and can put the skills on him/her after that so most likely Charlie so far only marked MC when visiting the orphanage...
Another thing these kids say is Valravn is immune to both Charlie's as Zara's skills... This could mean a possible way for MC to break any Taboo/geas/promise from Charlie or the mark from Zara.... He could be able to use memories from his fight against Valravn...
When Ella asks about MC's skills and you "reveal the extend of your powers" you get the dead end where she tells you MC was perfect from the start ;
Pretty much MC can copy "memories" of animals (monsters?) and not only apply them to himself but he can combine them too.... A really awesome skill if you at one point can use any defensive or offensive skills from your previous enemies...