Hidden toy (Halo 2: Anniversary)
From Halopedia, the Halo wiki
The hidden toys are Easter eggs in Halo 2: Anniversary. The eight toys included in the game are of the Master Chief, the Prophet of Regret, the Arbiter, Tartarus, Cortana, a rampant Cortana, the Librarian, and the Didact. They appear in remastered graphics on any difficulty.
The toys returned in Halo 5: Guardians and Halo Infinite as forge objects.
Delta Halo: Master Chief
Upon reaching the bridge, grab one of the Ghosts and follow the path back in the direction you came. When you reach the area of the path where you encountered the Jackal snipers, boost up the cliff wall. It is strongly recommended that you do this in Classic Graphics mode as this will show you the true level geometry on which the player must drive. Boost your way all along the ridge which rings around the lake until you reach the end of the rocky peninsula. Change to Remastered graphics and you will find the Master Chief toy sitting on the ground.
Regret: Prophet of Regret
The player must play with the Sputnik skull active in order to reach this toy; the Bandanna skull will also provide unlimited grenades for explosive jumping. From the start of the level make your way out of the structure, turn right, and grenade jump across the collapsed bridge. Grenade jump again up to the upper ledge of structure. From there, make your way along the walkway to the back of the structure where you will find the toy.
Sacred Icon: Arbiter
Near the beginning of the level the player will pass through two pistons into a large room where several Grunts and Jackals are being attacked by Sentinels. Move through this room across a small bridge and into a second, similar room. As the player enters the room, Tartarus will tell the player, "You're getting close to one of the shield generators. Many of my Brutes have fallen attempting to take it down. Let's see if you fare better." On the left side of the room there are a series of conduits sticking out of the wall above the player's head. Use a grenade jump to get up to the ledge (using the Sputnik skull will make this easier). The toy is in the far conduit on the left side of the room.
Quarantine Zone: Tartarus
At the very end of the level, once the gondola reaches the Library, the toy can be found on high ledge off to the right as the player exits the gondola and proceeds down the ramp. Grenade jump up to the ledge to retrieve the toy. It is necessary to play with the Sputnik skull active to achieve a large enough grenade jump.
The toy is found in the Valley of Tears A. Upon entering the area, proceed to the right and up the rocky face to the metallic platform which curves back toward the wall. The toy is found at the very end of the platform.
At the beginning of the chapter "Step Aside, Let The Man Through", once you exit the building, make your way toward up the rocks near the cliff edge. From there, grenade jump up to the very top of the cliffs. Follow the cliff ledge to the right until you are above the small Kig-yar encampment; off to the right, in a small alcove, you will find the Librarian toy. It is best to navigate the cliffs while in Classic graphics mode, as this will display the true geometry of the level. The Sputnik skull will make reaching the top the cliffs significantly easier.
High Charity: Rampant Cortana
The toy can be found in the chapter "Please, Make Yourself at Home" in the garden room with the stone arch. The toy is atop the arch.
The Great Journey: Didact
To access the toy's location, you must acquire a Spectre. This is most easily accomplished by taking over the Spectre at the beginning of the level. Leave it at the base of the cliff as you enter the structure. Once you meet up with Johnson, jump back down from the platform to where you left the Spectre. Drive the Spectre all the way through the level to the water near the entrance to the control room. Drive through the water to the very right of the map, where a land bridge juts up out of the water and curves back toward the control room. Follow this land bridge and use the Spectre to climb to the very top of the mountain behind the structure. The final toy sits on the summit. It is highly advisable to use Classic graphics mode when using the Spectre to climb the steep cliffs, as it shows the true geometry of the level.