Shifting

Each demon has a default form and a true form. A default form is seen on every plane and is the same across a whole subclass. A true form is unique to each demon and can only change from a major life event. Most demons have the same true form their entire lives. Demons are only able to recognize each other by seeing each other's true forms. It is immensely painful for demons to be trapped in a physical form of any kind, as the Other Place is not a material plane. Shifting grants a short release from the pain, but does consume mana. A shift consumes the number of mana points consistent with the level of the life form they have shifted to. Your form is an indicator of only what you look like, not what you can do. A demon in the form of a rat can still wield a longsword, etc.

Rules
You do not need to roll anything to transform back to your default form.You do not need to roll for a shift to a form of your current level or lower. To roll for a shift above your current level, roll 1d6 for your base roll. The modifier is determined by subtracting the level of the desired form from your own level. Add these two together. For instance, you roll a 5. Your level 4 character attempts to take a human form (level 7). The 5 is added to the -3, resulting in a 2. This indicates that you appear as a human at only the 1st and 2nd plane. In order to do this, you must also expend that level's number of mana points - in this case, 7. Above that you appear in your true form, which would allow others to identify you. Any form that doesn't seem to fit into a category is categorized by the GM's discretion.