Tear Asunder
Instant
Kicker 
(You may pay an additional as you cast this spell.)
Exile target artifact or enchantment. If this spell was kicked, exile target nonland permanent instead.
No one knew why the spiritmongers were so enraged by Phyrexian technology, but it was a stroke of good luck for the Coalition.
Illustrated by
Dominaria United#183UncommonJapaneseLegality
Rulings
If Tear Asunder is kicked, it can target any nonland permanent, not just an artifact or enchantment.
If a spell's kicker cost was paid, the spell is "kicked."
The kicker ability doesn't let you pay a kicker cost more than once.
If you put a permanent with a kicker ability onto the battlefield without casting it, you can't kick it.
If you copy a kicked spell on the stack, the copy is also kicked. If the copied spell is a permanent spell, the token the copy of that spell becomes when it enters is also kicked.
If a card or token enters as a copy of a permanent, the new permanent isn't kicked, even if the original was.
To determine a spell's total cost, start with the mana cost (or an alternative cost if another card's effect allows you to pay one instead), add any cost increases (such as kicker), then apply any cost reductions. The spell's mana value remains unchanged, no matter what the total cost to cast it was.