Warning: the following contains spoilers for Trollhunters: Rise of the Titans.
Avengers: Endgame, particularly Captain America and Doctor Strange's roles. Over the last five years, the Trollhunters franchise grew from the original Trollhunters: Tales of Arcadia series to include two sequel/spin-off shows, 3Below: Tales of Arcadia, and Wizards: Tales of Arcadia, before reaching its grand finale, tying all the shows and characters together (like Avengers: Endgame), Trollhunters: Rise of the Titans.
By its nature as the last movie in a shared universe, there were always going to be a lot of similarities to Avengers: Infinity War and Avengers: Endgame but Trollhunters took the similarities to the next level with some key plot elements and introduction of a particular MacGuffin. The most on-the-nose comparison comes at the end when Jim breaks open the Kronosphere to reveal the Time Stone, which most viewers likely instantly compared to the Infinity Stone by the same name in the MCU since it's around the same size and same shade of green. The fact that it came out of the Kronosphere, like how the MCU's Time Stone comes from the Eye of Agamotto at the end of Avengers: Infinity War only adds to the visual and thematic similarities.
The Trollhunters time stone doesn't only have the same name and look similar to the Time Stone into the Trollhunter amulet to go back in time to the very first episode of Trollhunters, making him the only person with a memory of all that happened throughout his tenure as the Trollhunter, serving as a sort of guardian of the timeline so he can help shape events in a new way that avoids the catastrophic conclusion of Trollhunters: Rise of the Titans.
Like Doctor Strange using the Time Stone in Avengers: Infinity War to glimpse 14,000,605 potential futures, enabling him to shape the outcome of Avengers: Endgame to the most ideal scenario, Jim knows what will happen in the future (although maybe a few million fewer permutations of it), and can use that to avoid calamity for some of his friends (particularly Toby). Meanwhile, at the end of Avengers: Endgame, Captain America also uses time travel (although it's through the quantum tunnel, not the Time Stone) to go back in time to place all the Infinity Stones where they belong, while also giving himself the life he was denied with Peggy Carter, also handing his shield to a new Captain America, Sam Wilson, AKA Falcon. In the same way, Jim goes back in time and approaches his future girlfriend Claire immediately and tries to introduce his mom to Stricklander earlier than before. He also has Toby become the new Trollhunter, although Toby doesn't know it's an inherited role since technically Jim never became Trollhunter in the first place in this timeline.
While some of the similarities may make Trollhunters: Rise of the Titans seem derivative, it's very much in the spirit of the show, which already embraces and homages numerous classical mythologies and modern intellectual properties, particularly Guillermo del Toro's films, with elements of Hellboy, Pan's Labyrinth, and a most successful franchise in history.
