Devastators is an epic undead unit that deals extra damage to structures and bases when it attacks them. The strength and ability of Devastators is increased when upgraded. Devastators fits into aggressive decks well.
Devastators's main purpose is for dealing extra damage to the base, so you should try to support it as much as possible.
Devastators pairs well with command effects from cards like Forgotten Souls or Herald's Hymn that immediately get it attacking the enemy base.
Another strategy is to buff and protect Devastators so that it can move into the enemy base on its own.
Devastators can also be used to remove enemy structures with its extra damage, like those built by Rockworkers.