Do not sign any contracts or agree to any bargains with faeries. Faeries love to haggle but will usually do so only if they are sure they will win. Do not eat or drink anything a faerie gives you. Do not go attend their magical revels under the hills. They will paint a beautiful picture of what awaits you there, but its beauty is false and hollow. Do not tease a faerie about their height. Do not expect direct answers to direct questions. Do expect indirect answers to indirect questions.
Superhuman physiology: Faeries possess unnatural swiftness and grace, strength and speed. They also have heightened senses, such as the ability to see in complete darkness, smell other things far away, and hear whispers a distance away with perfect clarity.
Accelerated healing: Faeries heal faster than humans due to their demonic heritage and powerful magic within them.
Magic energy: The fey's magic is believed to be unique in the world. It is very old and powerful, but neither seraphically nor demonically aligned. They can harness the powers of the world's ley lines, together with other strange magics. They possess magic that no one can fully understand, not even the Gray Book, which provides partly and imperfect ways to counter it.
Psychological manipulation: Faeries often use clever wordplay to their advantage in order to create loopholes. With their cruel sense of humour, they find delight in manipulating humans, both mundanes and Shadowhunters alike. Unlike full faeries, half-faeries can lie, and so they need not to weave lies into their sentences to hide the whole truth.
Longevity: Since the faeries live in a world where time flows slower, they seem to age much slower than the other residents of the Shadow and mundane worlds.