Lifespan

Some units have a limited lifespan, shown by a skull icon. At the start of the owner's turn, the unit's lifespan is reduced by one, and it's destroyed when it reaches zero.

Blockers with lifespan are vulnerable to chill, since freezing a blocker that's about to die anyway is equivalent to dealing damage. Similarly, absorb denial units like Bloodrager and flexible attackers like Scorchilla can reduce a lifespan unit's value as a blocker. For these reasons, it's sometimes better to attack with a lifespan blocker on its last turn even if the defensive value would be greater.