In Anima: Beyond Fantasy, magic is divided up into paths, some of which are opposed to each other. The rules quite clearly state that it costs twice as much to advance along a path opposed to one which a character has mastered… But they entirely neglect to define what constitutes mastery. (My suspicion is that something was lost in the game's translation to English.)
A mage's progression along a path is measured from 0-100, with a spell being learned every even-numbered level above zero. Presumably, therefore, path level 1 wouldn't consitute mastery in any sense.
However, I very much doubt that you have to reach level 100 to be a master, as the high end spells of the path ('Divine magic,' in game terms) are only usable by players with the aid of GM intervention – and the spells a little lower-level than that are 'High Magic,' which typically require characters to permanently give up their humanity before being castable. Since many of the powerful mages listed in the setting material do seem to still be human, presumably mastery does not require that level of path knowledge.
So, for rules purposes, at what point has a path of magic been mastered? I could easily houserule it, but if there's an official answer then I'd prefer to use that.
Best Answer
The Spanish version doesn't say anything of mastering your magic,
I will use google translator with the important part of the text, so you can see more or less what it is saying.
Spanish version: En el caso de que un personaje desarrolle conocimiento en una vía y posteriormente trate de dominar una opuesta, deberá invertir el doble de nivel de magia para mejorarla.
English version: In the case of a character in a knowledge developed way and then try to master an opposite must invest twice magic level to improve it.
It's a bit messy but it basically says that if you try to learn a path with points already invested in an opposite path you will have to spend twice the points. So, once you have spend one point (not even reaching the first spell!) in one path the opposed one (or ones in case of necromancy) will cost double.
I have been told that there will be some kind advantage with creation points that would help with this, but I haven't see it just yet (must be in Prometheum Exxet or something).