UngeheuerLich
Legend
Basically, non-Solo, Heroic tier monsters from MM1 should be fine without modifications, and, as mentionned, there's a few overpowered ones. Just go easy on the Brutes and Soldiers.
To expand on this, however, how is MM2? The math for Solos was changed here, but are MM2 monsters also underpowered?
The MM1 needed erratas from day one... actually before day one... I remember the preview video of chris perkins where he wanted to show a brute, opening the book at the hill giant entry and wondering how low the damage actually is and mumbling: 1d10+5 damage... yeah thats a lot...
MM2 in general worked usually as intended at that time. So for most monsters, the quick +1/2 damage per level fix could be used to get good challenging fights... some monsters may not even need that fix... Monsters that act twice or more a round should roll initiative normal and be given a second turn at +10 and their full alotment of actions each turn.
The bebilith acts on initiative 20 and 10 IIRC what is a joke at that level... the static modifier of all characters is higher than 10 by default...