If you hit an Eredar Lord with enough Wisps, it will explode. But why?
 How to get
With its zero mana cost, Wisp is primarily valuable for use as part of rogue combos, such as in a 'Miracle' rogue deck. It also works well with cards like Edwin VanCleef and Questing Adventurer which are improved by cards played. Wisps can also be incorporated into paladin deck using Divine Favor: dropping wisps and then casting Divine Favor will negate Wisp's card cost making it a free minion (0 mana cost, 0 card cost).
Such combinations aside, the Wisp's low stats and lack of useful abilities generally make it less desirable than other low cost minion cards.
Wisps are fey nature spirits who build night elf structures and gather resources. Wisps have the power to detonate, causing a backlash of mana, and can become Ancients. Several thousand of them, known as the "Ancestral Spirits", gathered at the call of the Horn of Cenarius to Nordrassil to destroy Archimonde.
Wisps are the form taken by night elves after death, equivalent to other races' ghosts. Wisps are able to move much faster than ghosts, aiding night elf adventures in returning to their bodies. According to legend, all wisps are the disembodied spirits of deceased night elves.