Knuckles: Buried Treasure is first Challenge Act for Sky Sanctuary Act 2 in Sonic Generations, as well as the second challenge act that Knuckles the Echidna appears in. As it is an Act 2 challenge act, it is only playable with Modern Sonic.
In order to pass this challenge act, the player must reach the goal safely with a total of 35 medals in his possession. However, the medals, which are indicated with special symbols, are buried deep in the ground, and the player has no means of reaching them himself. The solution to this problem is provided by pressing the Triangle/Y button to call upon Knuckles, who appears suddenly and digs into the ground directly behind Sonic. Should the player have positioned Sonic in the wrong spot, Knuckles will jump out of the hole in the ground and shrug, shaking his head. If there are medals in the ground nearby, however, a number of medals will pop out of the hole for Sonic to collect. Knuckles will then jump out of the ground, land, and disappear in a puff of smoke.
If the player does not collect the required amount of medals before reaching the goal, then he/she fails the mission and must try again to succeed. If the player has collected the required amount of medals, then he/she successfully completes the mission and proceeds to be ranked according to his/her time.