Inclusion Criteria:

          1. Patients who have unresectable Stage III through stage IV metastatic melanoma that
             have not received prior PD-1 directed therapy (Arm A) or that have progressed despite
             prior PD-1 directed therapy (Arm B).

          2. Be willing and able to provide written informed consent/assent for the trial.

          3. Be >/= 18 years of age on day of signing informed consent.

          4. Have measurable or evaluable disease based on RECIST 1.1.

          5. Be willing to provide archival or fresh tissue from a newly obtained core or
             excisional biopsy of a tumor lesion. Newly-obtained is defined as a specimen obtained
             up to 4 weeks (28 days) prior to initiation of treatment on Day 1. Subjects from whom
             newly-obtained samples cannot be provided (e.g. inaccessible or subject safety
             concern) may submit an archived specimen only upon agreement from the Principal
             Investigator.

          6. Have a performance status of 0 or 1 on the ECOG Performance Scale.

          7. Demonstrate adequate organ function, all screening labs should be performed within 14
             days of treatment initiation. Hematological: Absolute neutrophil count (ANC) >/= 1,500
             /mcL; Platelets >/= 100,000 / mcL; Hemoglobin >/= 9 g/dL or >/= 5.6 mmol/L without
             transfusion or EPO dependency (within 7 days of assessment). Renal: Serum creatinine
             </= 1.5 X upper limit of normal (ULN) OR measured or calculated creatinine clearance
             >/= 60mL/min for subjects with creatinine levels > 1.5 X ULN. Hepatic: Serum total
             bilirubin </= 1.5 X ULN or direct bilirubin </= ULN for subjects with total bilirubin
             levels > 1.5 ULN; AST (SGOT) and ALT (SGPT) 9 </= 2.5 X ULN OR </= 5 X ULN for
             subjects with liver metastases.

          8. contd from #7. Albumin >/= 2.5 g/dL. Coagulation: International Normalized Ratio (INR)
             or Prothrombin Time (PT) Activated Partial Thromboplastin Time (aPTT) </=1.5 X ULN
             unless subject is receiving anticoagulant therapy as long as PT or PTT is within
             therapeutic range of intended use of anticoagulants </= 1.5 X ULN unless subject is
             receiving anticoagulant therapy as long as PT or PTT is within therapeutic range of
             intended use of anticoagulants

          9. Female subject of childbearing potential should have a negative urine or serum
             pregnancy within 72 hours prior to receiving the first dose of study medication. If
             the urine test is positive or cannot be confirmed as negative, a serum pregnancy test
             will be required.

         10. Female subjects of childbearing potential should be willing to use 2 methods of birth
             control or be surgically sterile, or abstain from heterosexual activity for the course
             of the study through 120 days after the last dose of study medication. Subjects of
             childbearing potential are those who have not been surgically sterilized or have not
             been free from menses for > 1 year.

         11. Male subjects should agree to use an adequate method of contraception starting with
             the first dose of study therapy through 120 days after the last dose of study therapy.

        Exclusion Criteria:

          1. Is currently participating and receiving study therapy or has participated in a study
             of an investigational agent and received study therapy or used an investigational
             device within 4 weeks of the first dose of treatment.

          2. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any
             other form of immunosuppressive therapy within 7 days prior to the first dose of trial
             treatment.

          3. Has a known history of active TB (Bacillus Tuberculosis)

          4. Hypersensitivity to pembrolizumab, azacitidine, mannitol, or any of their excipients.

          5. Has had a prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study
             Day 1 or who has not recovered (i.e., </= Grade 1 or at baseline) from adverse events
             due to agents administered more than 4 weeks earlier.

          6. Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy
             within 2 weeks prior to study Day 1 or who has not recovered (i.e., </= Grade 1 or at
             baseline) from adverse events due to a previously administered agent. - Note: Subjects
             with ≤ Grade 2 neuropathy are an exception to this criterion and may qualify for the
             study. - Note: If subject received major surgery, they must have recovered adequately
             from the toxicity and/or complications from the intervention prior to starting
             therapy.

          7. Has a known additional malignancy that is progressing or requires active treatment.
             Exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the
             skin that has undergone potentially curative therapy or in situ cervical cancer.

          8. Has known active central nervous system (CNS) metastases and/or carcinomatous
             meningitis. Subjects with previously treated brain metastases may participate provided
             they are stable (without evidence of progression by imaging for at least four weeks
             prior to the first dose of trial treatment and any neurologic symptoms have returned
             to baseline), have no evidence of new or enlarging brain metastases, and are not using
             steroids for at least 7 days prior to trial treatment. This exception does not include
             carcinomatous meningitis, which is excluded regardless of clinical stability.

          9. Has active autoimmune disease that has required systemic treatment in the past 2 years
             (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive
             drugs). Replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid
             replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a
             form of systemic treatment.

         10. Has known history of, or any evidence of active, non-infectious pneumonitis.

         11. Significant active cardiac disease within the previous 6 months including: - NYHA
             class 4 CHF - Unstable angina - Myocardial infarction

         12. Has an active infection requiring systemic therapy.

         13. Has a history or current evidence of any condition, therapy, or laboratory abnormality
             that might confound the results of the trial, interfere with the subject's
             participation for the full duration of the trial, or is not in the best interest of
             the subject to participate, in the opinion of the treating investigator.

         14. Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial.

         15. Is pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial, starting with the pre-screening or screening visit
             through 120 days after the last dose of trial treatment.

         16. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent [for Arm
             A only].

         17. Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies).

         18. Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA
             [qualitative] is detected).

         19. Has received a live vaccine within 30 days of planned start of study therapy.