I've just started playing Anima: Beyond Fantasy and I'm particularly intrigued by the Mentalist, but I'm wondering if you need to take the Advantage "Free access to any Discipline" before you are able to buy affinity with disciplines and obtain powers and the like. I plan on making a character for a new campaign soon and don't want to start on the wrong foot.
Short answer, yes you need. There goes two character points.
Long answer, you can buy Access to one Discipline (for just one point, not two) and use only one Discipline of the mentalist.
Other characters without any of these two Advantages can only use one mentalist power with one specific advantage (don't remember the name) that let you use it at difficult, very difficult or impossible depending on the points spend in it.
Anyhow, without access to the Disciplines you cannot use your 'Psychic points' (sorry, but I own a Spanish copy and they are called 'CV', don't know the name in English... maybe WC?), for anything, or even helping other users of the Disciplines or linking / supporting to other Mentalists.