Wraith is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Menace

How it works : Wraith

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Wraith.

Minas Morgul, Dark Fortress

Minas Morgul enters tapped. {T}: Add {B}. {3}{B}, {T}: Put a shadow counter on target creature. For as long as that creature has a shadow counter on it, it's a Wraith in addition to its other types. (A creature with shadow can block or be blocked by only creatures with shadow.)

Accursed Duneyard

{T}: Add {C}. {2}, {T}: Regenerate target Shade, Skeleton, Specter, Spirit, Vampire, Wraith, or Zombie. (The next time it would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Nazgûl

Deathtouch When this creature enters, the Ring tempts you. Whenever the Ring tempts you, put a +1/+1 counter on each Wraith you control. A deck can have up to nine cards named Nazgûl.

Lord of the Nazgûl

Flying Wraiths you control have protection from Ring-bearers. Whenever you cast an instant or sorcery spell, create a 3/3 black Wraith creature token with menace. Then if you control nine or more Wraiths, Wraiths you control have base power and toughness 9/9 until end of turn.

In the Darkness Bind Them

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after IV.) I, II, III — Create a 3/3 black Wraith creature token with menace. The Ring tempts you. IV — For each opponent, gain control of up to one target creature that player controls until end of turn. Untap those creatures. They gain haste until end of turn. The Ring tempts you.

Sauron, the Necromancer

Menace Whenever Sauron attacks, exile target creature card from your graveyard. Create a tapped and attacking token that's a copy of that card, except it's a 3/3 black Wraith with menace. At the beginning of the next end step, exile that token unless Sauron is your Ring-bearer.

Canoptek Wraith

Wraith Form — This creature can't be blocked. Transdimensional Scout — When this creature deals combat damage to a player, you may pay {3} and sacrifice it. If you do, choose a land you control. Then search your library for up to two basic land cards which have the same name as the chosen land, put them onto the battlefield tapped, then shuffle.

Wraith, Vicious Vigilante

Double strike Fear Gas — Wraith can't be blocked.

Witch-king, Sky Scourge

Flying Whenever you attack with one or more Wraiths, exile the top X cards of your library, where X is their total power. You may play those cards this turn. Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)