Currently a part of a 20th level campaign as a playtest for two of my homebrew classes (the Spellblade class and the Force Missile Mage subclass of Wizard) and I have to say, these have been much more challenging and therefore appropriate to our level than the Tarrasque as written in the Monster Manual for example. Our 5-man party had to fight the Terrasque and Tiamat simultaneously to truly feel challenged before finding your thread. Of course, my group enjoys optimising down to the last minute detail, as a full party no less, so we desire more difficult challenges in combat to the vast majority of tables and your monsters haven't let us down. We haven't dared to take on any monsters above CR 30 though. We are considering increasing party size and/or introducing a homebrew system to level up beyond 20th before we do that.
