"Monster"-class enemies are basically a tiny step-up from "Archvillains", so they're not exactly standard enemies. I can't remember if they turn into EBs or anything depending on difficulty though. :3
Only thing I can suggest is to not have them as mission objectives if you want them in your mission.
Ideon's Paragonwiki page
Member of Paragon/Rogue Knights
Arc: 60092 - Supa Rumble in the Park
"Keep living the dream, and never let any jerk tell you what to do."
-- High-Roller
I played with the Quarry GM in a for fun mission a while back. They do not scale down and are quite powerful.
One Quarry smacked around 5-7 Lord Recluse AVs with Bane ambushes. Was fun to watch 
Giant Monsters will not scale below Monster rank in MA missions.
Thanks to you all for your responses; I would like to use one but I agree with the comment not to use them as an objective, otherwise this mission will never end..thx!!
Arc: 378122 "Tales of the Terran Space Marines -The Apocalypse Initiative" 5stars!
http://www.youtube.com/watch?v=6Rgl4...687B0FC89F142C
Arc: 481545 "Twilight of the Gods - The Praetorian conflict"8000+ hits!
http://www.youtube.com/watch?v=XxJ6S...848B21E2350DCC
Want to use one of the DE monsters in a story, however, is there any way to reduce its defense/power? Usually takes quite a bit of time to take them down, so wanted to see if there was a way to adjust even though they are standard characters..
Arc: 378122 "Tales of the Terran Space Marines -The Apocalypse Initiative" 5stars!
http://www.youtube.com/watch?v=6Rgl4...687B0FC89F142C
Arc: 481545 "Twilight of the Gods - The Praetorian conflict"8000+ hits!
http://www.youtube.com/watch?v=XxJ6S...848B21E2350DCC