This is my entry to David Flor's contest for building a Solo monster encounter, complete with a pool! This encounter was built using the Angry DM's D&D Boss Fight method and the monster stat blocks were built using Power 2ool. I highly recommend using Power 2ool, especially if you have access to the Dungeons and Dragons Insider compendium.
Click HERE for the encounter.
Edit: It should be noted that the last form of Grimthyr (called Grimthyr, Bloodied) is, for all intents and purposes, mechanically considered Bloodied.