Naru Meha enters the battlefield, it triggers, copying Vantress Visions, with the copy targeting
Karn's ability.
Resolve the copy of
Karn's ability, adding ({C} magic symbol) for each artifact you control.
Repeat from step 4.
If you control four or more artifacts, this combo nets infinite colorless mana, which can be used to copy Vantress Visions infinitely targeting any other abilities on the stack, or to blink any number of creatures infinitely.
Results
Infinite blinking.
Infinite colorless mana.
Infinite copies of abilities you control on the stack.