Interceders are those witches that specialize in magic dealing with other planes and dealing with the entities that reside on them. Many dedicate themselves to maintaining proper planar boundaries and regulating what is allowed to pass between them, though others take a more permissive approach, often to plunder these strange and otherworldly realms for personal power and allies.
When you select this archetype at 2nd level, you have advantage on persuasion, intimidation, insight, and deception checks made when dealing with fiends, celestials, fey, elementals, or aberrations and advantage on saving throws against their abilities.
You also learn one of the following languages: primordial, sylvan, infernal, abyssal, deep speech, or celestial, and add the following spells to your spell list which count as witch spells for you: conjure woodland beings, conjure minor elementals, conjure celestial, conjure fey, conjure elementals, infernal summoning, conjure fiend, conjure horde demon, and conjure greater demon.
At 6th level your familiar may instead take on any form allowed by the warlock Pact of the Chain feature.
At 10th level you always have the banshment spell prepared and it doesn't count against your number of prepared spells. If you cast banishment at 5th level or higher on a creature that is not on its native plane and it fails its save, the duration remains 1d4 + 2 rounds but the penalty on subsequent saving throws increases by 1 per slot level above 4th. Such a creature that critically fails its initial saving throw against a banishment spell cast by you is permanently banished, with no need to wait out the duration or maintain concentration, regardless of what level you cast it at.
At 14th level you always have the planar ally spell prepared and it doesn't count against your number of prepared spells. You may cast it once per long rest without expending a spell slot. The cost of any service provided by an ally summoned by the planar ally spell when cast using this ability is halved.