Magic
Magic has many forms in the Gargoyles Universe, but two specific variants stand out above others: human magic and faerie magic.
Mortal magic
Mortal magic is generally worked through spoken incantations, recited in an ancient language - usually Latin, although in at least one case, the spells involving the Golem, the language in question was Hebrew. From what we can tell, it seems that only such languages can be used to work human magic, rather than comparatively young ones such as English. A human wizard’s spell usually has to be activated through a magical object of some sort, serving as a conduit, such as the Grimorum Arcanorum.
Human spells often have counterspells, but these can be tricky in undoing enchantments. In general, the preferred way of undoing a spell is to discover a means for its breaking within the very incantation, and fulfill that condition through mundane means. Thus, Xanatos broke the Magus’s curse of perpetual stone sleep upon the gargoyles by making Castle Wyvern rise above the clouds (i.e., moving it to the top of the Eyrie Building), and later, with the gargoyles’ help, broke Demona’s curse of "stone by night" upon New York by making the skies burn (with the help of some jet packs filled with a harmless hypergolic gas). Elisa undid Demona’s spell of mind control upon Goliath through a cunning stratagem; she ordered him to act for the rest of the life the way that he would if he was not under a spell.
According to Hudson, in order to be affected by magic, one has to both see and hear it; at least, this was the case with Demona’s "stone by night" spell, which consequently did not affect Jeffrey Robbins because he was blind. It is uncertain if this is the case with all human spells, since the "spell of humility" that the original Magus cast upon all gargoyles certainly extended all over the world, far beyond the bounds of the Roman Empire.
Mortal magic can also be practiced by gargoyles, although they do not take up the study very often (Demona and Una being currently the only exceptions known to us).
Actually making use of magic seems to be quite tricky, from the evidence; it is apparent that only a practicing sorcerer can handle a spell or magical device properly. (Hence Xanatos’s refusal to make use of the Grimorum as a means of undoing Demona’s "stone by night" curse). Demona described the spell that she placed upon Goliath to control him as complex, even though it consisted of only a few Latin words. Presumably much of magic has to depend upon training in such matters as correct pronunciation and gestures.
Known practitioners of mortal magic include the Magus, the Archmage, Demona, Macbeth, some anonymous sorcerers in Constantine III’s service mentioned by the Magus, Rabbi Loew, Una, the Aborigine shaman who served as Dingo’s mentor in Australia, the Mayan wizard who crafted the Mayan Sun Amulet, and the Roman Magus. Merlin may count as well, although this is uncertain at present, owing to his halfling heritage.
Faerie magic
Faerie magic is the inherent ability of all members of the Third Race. It is generally activated by the fay in question uttering a rhyming couplet or two, although occasionally without words, or, in the case of Oberon, a single word. (During his "enhanced" period, the Archmage could also cast spells with but a single word, an indication of his great power). Judging from Alexander’s case, the same applies to halflings as well.
Faerie magic cannot directly affect anything made of iron. However, the fay can get around this restriction through such methods as striking iron objects with powerful gusts of wind (as Oberon did to Xanatos when the latter was wearing an iron exo-suit).
Further information about faerie magic can be found in the entry on Oberon’s Children.
Other notes on magic
According to Xanatos, "mixing magics is dangerous." Presumably, this applies in particular to mixing mortal magic with faerie magic, although it could even apply to mixing two pieces of mortal magic, given that the context in which he uttered this statement was Owen’s suggestion of using a spell in the Grimorum Arcanorum to undo Demona’s "stone by night" curse upon New York.
Beyond faerie and mortal magic, there are other forms. It is rumored that the Space-Spawn may have practitioners of alien sorcery, although this has yet to be confirmed. Ghosts, such as those of Hakon and the Captain of the Guard, have intrinsic magical abilities, such as being able to conjure up illusions or temporarily possess people. Objects can be charged with magic: among these are the Grimorum Arcanorum, the Eye of Odin, the Phoenix Gate, the Cauldron of Life, the Mayan Sun Amulet, the Praying Gargoyle, the Medici Tablet, the Scroll of Thoth, the Stone of Destiny, and maybe Excalibur. (Not every object in the possession of a wizard is necessarily magical, however, as witness the Scrolls of Merlin). Certain places can also become charged with powerful magic, such as the Archmage’s cave. Some such places even gain a certain atmosphere of holiness, a sense of connection with God, and humans build temples and churches in such places. As a result, some forms of magic need to be cast on holy ground, such as Demona’s use of the Fulfillment Spell (which she cast in St. Damien’s Cathedral).
Further information about magic can be found in the specific entries on individual magic-users or artifacts.