Was Mariette a Replicant?

Mariette (Mackenzie Davis) is a replicant prostitute, and secretly a member of the replicant underground. Joi wants to experience sex with K, but the holographic projection of her AI lacks physical substance, so she hires Mariette to have sex with him – while overlaying her projection on Mariette's body.

Is Deckard a human or replicant?

Deckard takes the Voight-Kampff test and passes, confirming that he is a human. Harrison Ford, who played Deckard in the film, has said that he did not think Deckard is a replicant, and has said that he and director Ridley Scott had discussions that ended in the agreement that the character was human.

What did Mariette put in K's pocket?

Yeah it's a tracking device, it's how they found him in Vegas after he was left there (because he was a "bad dog") by Luv.