After a quick google found these codes - No idea what they did but they all redeemed ok..
Date (MM/DD/YY) Promotion/Link/Code Expiration Reward Notes
04/03/14 INSTITUTE - Taskmaster's Mystery Box 1 x Credit Drop Boost 2 hours, 1 x Rarity Drop Boost 2 hours, 1 x Special Item Find Boost 2 hours.
04/06/14 RECRUIT - S.H.I.E.L.D Agent Preparedness Kit S.H.I.E.L.D Agent Preparedness Kit
05/23/14 2015 - 3 x Fortune Cards Fortune Card Mark II, Fortune Card Mark I, Fortune Card Mark V
05/30/14 BEWORTHY - Odin's Bounty Boost Odin's Bounty Boost
06/05/14 GLASSCANNON - Experience Boost - 2 hours Experience Boost - 2 hours
06/05/14 ANIRUOK - Omega Point Box Omega Points (5)
Date (MM/DD/YY) Promotion/Link/Code Expiration Reward Notes
04/03/14 INSTITUTE - Taskmaster's Mystery Box 1 x Credit Drop Boost 2 hours, 1 x Rarity Drop Boost 2 hours, 1 x Special Item Find Boost 2 hours.
04/06/14 RECRUIT - S.H.I.E.L.D Agent Preparedness Kit S.H.I.E.L.D Agent Preparedness Kit
05/23/14 2015 - 3 x Fortune Cards Fortune Card Mark II, Fortune Card Mark I, Fortune Card Mark V
05/30/14 BEWORTHY - Odin's Bounty Boost Odin's Bounty Boost
06/05/14 GLASSCANNON - Experience Boost - 2 hours Experience Boost - 2 hours
06/05/14 ANIRUOK - Omega Point Box Omega Points (5)