Okay, made it to the final stage of the Ursa fight.
 
It starts off at 400 health. With Tempest’s base attack power at 12 and a regeneration time of every 2 hours, that means it will take about 68 hours to take the Ursa down. Meanwhile, to earn the Tempest prize, you have to complete the fight within 3 days, or 72 hours.
 
In this match, her partners are Discord (normally 600 gems, and as of writing, on sale for 420 gems) and Daybreaker (1000 gems, or $30 in her bundle). Having just Discord (providing 12 attack power) will cut the time needed to bring the Ursa down in half, whereas having Daybreaker (providing 46 attack power) will make it a cakewalk.
 
You’ll notice that this is a very deliberate ploy to force you to spend gems.