Toy Story That Time Forgot, on ABC
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This is the second Toy Story TV special; it first aired on December 2, 2014. It's technically a Christmas special because it aired in December and because the story takes place shortly after Christmas, but there's really nothing particularly Christmasy about it. I should also mention that it's set after Toy Story 3, so the toys are currently owned by a little girl named Bonnie. Trixie the Triceratops is a bit disappointed that when Bonnie plays with her, she always imagines Trixie as something other than a dinosaur. (In an amusingly ironic twist, just when she thinks Bonnie is finally going to play with her as a dinosaur, Bonnie instead treats a small "Angel Kitty" Christmas ornament as a dinosaur. Incidentally, even though Angel Kitty doesn't have many lines of her own, I quite liked this new character, as she was adorably philosophic.)

But then Bonnie goes for a play date at the house of her friend Mason, who's just gotten an awesome new video game for Christmas. While Bonnie joins him in playing that, Trixie and some of Bonnie's other toys are left to explore Mason's toy room on their own. They soon meet a tribe of bipedal dinosaur toys called Battlesaurs, who take Trixie and Rex into their tribe, but separate them from the other toys. Trixie befriends a Battlesaur named Reptillus Maximus, but she eventually discovers that he and the other Battlesaurs don't know they're toys, since Mason has never played with them. So they take their warlike society very seriously, although actually they're being controlled by an elder dinosaur (or something) called the Cleric, who does know that they're all toys, but doesn't want them to know that. And the Cleric has nefarious plans for Trixie and her friends, which she has to prevent, by revealing the truth to Reptillus. And in teaching him, Trixie learns a valuable lesson, herself.

So, it's a pretty fun story, with a happy ending. I don't really see it becoming a holiday classic, or anything, but it's a worthy entry in the franchise... and appropriate for any time of year.