The game's objective is to win the match by not being the player holding the bomb when the time ends.
The main challenge is to either run away from the player with the bomb or chase another player to pass him the bomb. This is the main challenge and is also the Core Gameplay Loop of the game.
Other then that, we have the situational challenges, such as the rolling ball on the necromancer level.
The intrinsic rewards of the game are from within the player have without any external input. It is relaed to the gameplay itself.
The extrinsic rewards are related to things outside the player, like when the game says you won.