Heroes of the Storm's Garden of Terror thinks it has its hook: a night-and-day sequence.
Unlike the mostly cosmetic lighting filters in MMO day/night cycles, Garden of Terror's transition between the two will change the fundamental rules of the match. While during the daytime players can check out mercenary camps, the nighttime is a whole different story. The camps go away when the sun goes down, and out pops nighttime horrors as players' visibility decreases. The daytime only comes back when all of the horrors are killed, giving players control over how long the dark lasts.
One of the Garden of Terror's objectives is gathering up seeds to plant so that a huge player-controlled mob can be summoned. Learning when and how to use the summon will be a key to dominating the match.