Seems a great deal. Basically see any 3 films of 17 listed between now and the end of March, save the stubs, put them in ticket wallet, and you can see any of the listed films in 2D free by end of March. You can even see multiple films on 1 day to earn.
"How to claim your free ticket
1) Pick up one of our awards ticket wallets in cinema
2) See 3 of our 17 awards films before March 31st 2017
3) Collect your ticket stubs
4) Exchange your 3 tickets stubs and wallet for a free 2D ticket at the box office or retail counter
Award Season Films: La La Land, A Monster Calls, Manchester By The Sea, Billy Lynn's Long Halftime Walk, Lion, Jackie, 20th Century Women, Silence, Hacksaw Ridge, Miss Sloane, The Founder, Fences, Moonlight, Loving, Gold, Toni Erdmann, Hidden Figures.
*The offer is valid from January 1st to the 31st of March. Tickets must be collected for performance between Jan 1st and March 31st."
More T+Cs which I feel are important:
"Only fully priced tickets are eligible for this promotion. This includes Adult, Teen, Child, Student and Senior ticket types. Family Tickets are excluded from this promotion.
5. Tickets can be collected on any screening format or premium offering, including 2D, 3D, IMAX and ISENSE.
6. Tickets must be collected at time of visit to the Box Office, retail counter or Guest Service point only. Online booking confirmations cannot be included. No alternative will be accepted.
7. Tickets collected on Bargain Days will be included.
8. Tickets from any promotional offer cannot be included. This includes Meerkat Movies, Tesco Clubcard, Times 241 or any other promotional offer.
9. Tickets collected on ODEON Silver Cinema or ODEON Screen Unseen are excluded.
10. Tickets purchased with a Limitless card or OPC points are excluded."