Activate Karn by paying ({1} magic symbol) , causing Caged Sun to become an artifact creature until end of turn.
Activate Caged Sun by tapping it, adding ({G} magic symbol) .
Caged Sun triggers, adding ({G} magic symbol) .
Repeat step 2.
As Caged Sun's triggered ability is a mana ability, this combo creates a mandatory infinite loop that cannot be interacted with, thus ending the game in a draw.