In Sorcery, if there is zero of something, the game considers that thing to not exist at all. For example: If a unit takes zero damage, then it did not actually take any damage at all. Triggers looking for damage wouldn't be satisfied. If a unit takes zero steps, then it did not move at all. Triggers looking for movement wouldn't be satisfied. If you draw zero cards, you did not draw any cards at all. Triggers looking for card draws wouldn't be satisfied. etc. There are two notable exceptions: It is possible to strike for zero damage, e.g. Grandmaster Wizard. The unit still made a strike for effects that are looking for strikes (e.g. Phantasmal Shade), but the strike didn't do any damage at all. It's possible for units to have zero power and still exist in the realm. Units with 0 power (e.g. Grandmaster Wizard) only die if they take damage (1 or more). A spell cast for zero mana does not require any mana at all to cast, but it still counts as a cast spell.