Magic in all of the realms requires a fuel, from there of which it can translate into very powerful, dangerous energy. Different realms have different strong points in how the output of energy can be translated, as each of the four realm has a particular fuel source. The magic from one realm can be used on another, however this can only be utilized by a creature that originated from the original realm. But, a creature cannot go to another realm and utilize that realms magic. For example, a creature tied to the Earth cannot use Underworld magic, even if they ingest the proper fuel for it. Their systems are not compatible. Whereas a creature from the Fae Realm can still cast its magic on Earth. However, creatures should always be mindful of the availability of fuel.
Hybrids are very strange when it comes to this–a hybrid of two creatures from different realms generally can only use one realm’s magic their entire life. However, there are exceptions to this, in which anomalies run amok.
Some types of magic overlap through all realms, and some show more strongly on some as opposed to others. The realm sections of magic in this section will go over the specifics.
The two types of magical outliers with no origin to any realm are: Ancient Magic and Magical Vampirism(not to be confused with the species Vampire, of course). Details will be provided on both of these, but the way to use it is the same across all realms. Both are extremely dangerous.
Caution should be used when casting magic. There are always drawbacks if the user is not an advanced mage with many years of practice behind them. Luckily, for every drawback, there tends to be a solution. However, all advanced magic users specialize in one type of magic. Too many can overwhelm the user, preventing them from protecting themselves from magical drawbacks. Each drawback is unique and will be explained in the appropriate sections.