Polaris, the Frozen Guide

Whenever a creature you don't control becomes
tapped due to a source you control, Polaris, the
Frozen Guide explores.

Whenever a player expend 4 during their turn, tap
up to X target untapped creatures that player
controls, where X is 1 plus the number of snow
counters on Polaris. If that player is you, instead put
a snow counter on Polaris. (A player expend 4 as
they spend their fourth total mana to cast spells
during a turn.)