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All spirits will manifest to you in their own way, and in their own time. Spirits can manifest in their true form, in various animal/creature forms (especially polymorphers), as Shades, mist, orbs, light streaks, shadows... there are many ways.
Not all spirits are wish-granters, in fact, most of them are not. The ability to grant the wish of someone is a specialized gift. If the entity in life did not have the ability, they will be graced with additional abilities simply because they died. In the case of Immortals (gods & goddesses) they are not wish-granters. They can influence your life, they can help you see what you need, they can help you discover things about yourself or opportunities in your life, but they aren't what are classified as wish-granters.