Lairwatch Giant can block an additional creature. Whenever Lairwatch Giant blocks two or more creatures, it gains first strike until end of turn.
A giant can brood over a grudge for decades, and woe to those who interrupt him.
Official Rulings for Lairwatch Giant
10/1/2007 : Lairwatch Giant's second ability triggers if it blocks at least two creatures when blockers are declared. It will also trigger if it blocks fewer than two creatures when blockers are declared and effects then cause it to block more creatures. However, if Lairwatch Giant is already blocking two or more creatures, and effects then cause it to block more creatures, the ability won't trigger again.