I realize it'll be a long time before we'd see any such thing, but has Mike (or anyone else at Wizards) said anything to suggest there'll be monster conversion guidelines from 3E?
I'd really like to switch my current campaign to 5E at some point, but I'm using a lot of obscure aberrations from later 3E books and Pathfinder...
Someone posted a 3/3.5 monster conversion document in one of the other monster threads. It is fairly technical, and will help you until August 8 when some monsters are added to Basic D&D.
In the case where the monster exists in the Starter Set (and soon D&D basic), just use the 5e version and increase or decrease the number to get the difficulty you want. Otherwise, you can start by using one of the Starter Set monsters as a base. Or, if you copy over the monsters hit dice, ability scores armor and weapons, you can then determine all of its modifiers, HP and AC under 5e. You can then copy over special abilities that work under 5e. A lot of monster special abilities will become proficiencies or advantage. This has been my general strategy for Age of Worms, a 3/3.5 campaign, and it has held up in the first two chapters. For instance, for Grimlocks, I took the Orc as a base. I copied over the Grimlock's ability scores, armor and wepons. Blindsight carried over. The +4 natural armor became a +1 to fit more in bounded accuracy. The Grimlock became immune to the blinded condition because he has no eye and uses his hearing and smell instead. This also meant he should be vulnerable to thunder in my opinion. That plus the stealth skill and he was done.
You don't have to get it perfect. Nobody will no the difference. In a couple of weeks there will be monsters in D&D basic, and the Monster Manual comes in October.
