Speculah:Kyubey is Evil Theory

This is one of the very first speculations that have appeared, and also one of the most commonly accepted. This theory states that Kyuubey isn't as cute and inoffensive as he looks. First of all, he seems a bit too pushy towards Madoka and Sayaka (for example, at the end of episode one, he says "I want you to become magical girls", which somehow shows his true intentions). All the more, it seems suspicious that he will grant wishes and turn people into magical girls without asking anything in return. So the theory is that Kyuubey either acts according to his own interest, or is the "messenger" of a greater entity that has its own whereabouts.

However, although it is commonly accepted that Kyuubey (and therefore Mami since they're allies) is evil, opinions differ as to what his goal are or what benefit he could make from turning people into magical girls.

In fact, this theory evolved with episode 2. We now think it is possible that Kyuubey (or whatever entity he is working for) may be interrested in Grief Seeds, or the "mud" that they contain. Moreover, if the "witches are fallen magical girls" theory is true, then it is possible that Kyuubey creates magical girls so that they supply him with "black mud":

1. Grant wishes and create magical girls
2. Wait for these magical girls to turn into witches
3. Create more magical girls to fight the witches
4. Collect the "black mud" the new magical girls have found
5. Repeat process

Please also note that in this theory, the dream shown to Madoka at the beginning of episode 1 may as well be a fake dream, created for the only purpose of making Madoka want to be a magical girl. That supposes Kyuubey can alter people's perception, which is also fairly possible since he's able to communicate by telepathy.