For the purposes of encounter building and rewards, a solo monster counts as five standard monsters.
Combined with another role (a solo lurker, for instance) but contains elements of other roles
Deals five times the damage of a standard monster
Lasts five times as long as a standard monster
Tip: Use one solo monster as an entire encounter, or pair one with minions or one or two standard monsters.
Published in Rules Compendium, page(s) 288.