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.