This time around I decided to move away from the Monster Manual and delve into Mordenkainen’s Tome of Foes with the Astral Dreadnought. This gargantuan monstrosity born from the deepest recesses of the Astral Plane seeks nothing but the destruction and consumption of the nearest entity. The Dreadnought was introduced on the cover of the Manual of the Planes release in 1987 but did not receive playable stats until the 2nd edition of the same supplement. Early versions of this monster adopted simple yet effective tactics to overcome enemies but since then they have been made much more lethal and far more interesting.
An Astral Dreadnoughts arsenal includes some extremely large crab claws, a massive maw, and some magical defenses including an anti magic cone and access to a demiplane. Similar to a Beholder, a Dreadnought emits an anti-magic cone from its eye that spreads in a 150 foot cone. This includes not just spells from a spellcaster but all magical items are nullified. So if you were hoping to blast off all the charges from a wand of fireball, you might have a tough time. If you are going through the Astral Plane through some sort of spellcasting more than likely you will take your astral form. With this comes an extremely vulnerable weakness in the form of a silver thread that connects you to your material body. The Dreadnought will target this and if it is severed, you are finished. What I think is the most amazing thing about this monster is that when it consumes someone rather than slowly digested they are transported into a harmless demiplane that for all intents and purposes resembles a simple stone room. There is no way of exiting aside from a spell that enables planar travel and doing damage to the room does not effect the Astral Dreadnought.
If you are planning on going into the Astral Plane I have a few suggestions: The first being just don’t do it. There are a lot of things in the Astral Plane and this is only one of many terrible things waiting there. Another suggestion would be to blind it as soon as you are able and as often as you can thereafter. Disabling that anti-magic cone is crucial. Next would be to bring as many buffs as you can. Dreadnoughts are not susceptible to many conditions so dealing big damage is the way to go. Go into the unending oblivion with a little bit of knowledge to help you on your way, and good luck.
The Dungeoneer's Journal 