DM's Guild Author
But can you use any monster from previous D&D material that you like in your products? No copyright strikes? I know Paizo can't use anything other than the ones that may be used?
If you can use anything you want that is really awesome and I'm really rooting for the Metalmaster and Deadly Dancer and a more mantis-like Ethereal Slayer to make it in your next book! (just search a picture of the deadly dancer, it is one of the most beautiful things i've seen, so bizarre and special!
As long as it is IP owned by WOTC and in the allowed settings set in DM's Guild, then yes, we can use it. As long as you release through the DM's Guild, you're not limited by the OGL.