Desperate Lunge

• WWizards of the Coast2019-05-03
  Official Ruling
  A creature gaining flying after it has been blocked by a creature without flying or reach won't remove the blocking creature from combat or cause the creature it blocked to become unblocked.
• WWizards of the Coast2019-05-03
  Official Ruling
  If the target creature is an illegal target by the time Desperate Lunge tries to resolve, the spell doesn't resolve. You don't gain 2 life.

Rulings via Scryfall