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Invasion from the Planet of Tarrasques
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Invasion from the Planet of Tarrasques


Invasion from the Planet of Tarrasques is a single-session, over-the-top, gonzo action adventure meant for four to six level 20 characters. The adventure serves as a capstone for Waterdeep: Dragon Heist and Waterdeep: Dungeon of the Mad Mage, but can be modified for any setting.

What’s more fun than one tarrasque? How about multiple tarrasques stomping across Waterdeep? How about a whole planet full of tarrasques ready to rumble? If that sounds exciting, then Invasion from the Planet of Tarrasques is for you.

Halaster Blackcloak died... but then he came back... with reinforcements...

Adventure Background

Halaster Blackcloak, the Mad Mage of Undermountain, always has a contingency in place. As long as Undermountain remains beneath the city of Waterdeep, Halaster can never truly die within its walls, for the dungeon rebuilds the mage’s body on the rare occasions when adventurers “kill” Halaster.

Halaster realized that if adventurers destroyed all of Undermountain (a nigh impossible feat more difficult than even slaying the mage), he would lose his immortality. To further protect his life, Halaster took some of the rooms and halls of Undermountain and flung them across the multiverse, including other worlds of the Material Plane. With Undermountain spread across existence, the task of permanently killing Halaster is even more difficult.

Unfortunately for the mage, a party adventurers recently killed him in his dungeon beneath the City of Splendors. When Halaster’s body reformed, he found himself in Falx, another world of the Material Plane inhabited entirely by enormous, carnivorous monsters with endless appetites. These scaly bipeds are closely related to the tarrasque, an infamous monstrosity feared across the worlds of the Material Plane. Halaster, now obsessed with punishing the adventurers who killed him, began to hatch a plot. If one tarrasque could level an entire city, what could a planet’s worth of the beings do to Faerûn?

Adventure Overview

This adventure is divided into three chapters.

  • Chapter 1. In “Giff You a Hand” a platoon of giff arrive in a spacefaring vessel and warn the adventurers about a coming invasion of tarrasques. With the clock ticking, the characters have a chance to prepare for the battle by mustering their allies.
  • Chapter 2. In “Battle for Waterdeep” the characters face-off with the invading titans, defend Waterdeep, and fight for their lives.
  • Chapter 3. In “Falx, Ho!” the characters travel through a portal to the planet of Falx to face Halaster and his army of tarrasques atop a stone tower made from pieces of Undermountain.

This product includes...

This is a DMs Guild Adepts product. The DMs Guild Adept Program was started and is managed by Wizards of the Coast. It brings together some of the best talents creating for the DMs Guild for creative development. DMs Guild Adepts products are identified by the gold ampersand logo.

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Reviews (9)
Discussions (8)
Customer avatar
Vincent K August 11, 2022 1:03 pm UTC
I'm about to run this for 5-6 players, I don't see anything for recommend level of magical equipment though. Typically I have pretty low magic item usage in my campaigns/one-shots- 2 uncommon magic items and 1 rare item is what I was thinking- is this too low/would this be unreasonable? Curious to hear what other DM's who have run this would have to say about their PC's starting magic items
Customer avatar
Jacob R June 20, 2022 8:53 pm UTC
I just DM'd this as a one-shot (my party wanted to build some superhero-tier characters and I want to let loose the BIG GUNS on them) and WOW did we have a blast. None of us had never faced / used an actual Tarrasque in play before (much less the five I sent against them) and the ones who thought they knew the monster were surprised at the additional special abilities. This is an excellent module for over-the-top good times. Thank you for creating this.
Customer avatar
Leonardo J December 22, 2019 2:40 am UTC
I had some problems understanding the layout of the tower. What is the scale of that map? How large is the top of the tower?
From the drawing I can’t understand how even one Tarrasque would fit on top of the tower!
Customer avatar
John M March 23, 2019 4:11 pm UTC
This is the most ridiculous, gonzo thing I've ever heard. Which means I _must_ buy it. Now. I would love to see this in a book, booklet, or some type of physical form. Perhaps the writer can extrapolate extra pages to make it happen.
Customer avatar
Jocelyn R March 16, 2019 3:52 pm UTC
Grabbed this as part of the RAINN bundle, and while it'll take months, maybe even a year or two, to run it, I'm looking forward to it as an Epilogue to my group's DotMM campaign. We're only on level 2 of the megadungeon, but I've begun sowing the seeds for this, and have plans to drop ever growing hints in the months to come.
Customer avatar
James I March 25, 2019 9:51 pm UTC
I can't wait to hear more!!
Customer avatar
David S January 08, 2019 4:52 pm UTC
Are you ever going to make this Print on Demand?
Customer avatar
James I January 16, 2019 1:26 am UTC
Hey David! Probably not. The product is not long enough for it.
Customer avatar
David S November 26, 2020 1:29 pm UTC
I just looked and Kobold Press's "Genies Great and Small: 21 New Genies of Zakhara" is one page shorter than "Invasion from the Planet of Tarrasques" and available on Print on Demand:

I would really like to be able to buy a dead-tree copy to put with my Spelljammer collection. :-)
Customer avatar
Luciella S November 17, 2018 8:42 pm UTC
Leaving a comment rather than a review since I haven't actually run this module.

I haven't played and don't have copies of Waterdeep Dragon Heist or Dungeon of the Mad Mage and bought this assuming that I could still run the adventure regardless, but honestly I don't think I can, at least without either doing a heap of research or making up a lot of stuff. The text assumes a great deal of knowledge about Waterdeep and its defences and inhabitants. For example, I have no idea what the walking statues are or the personality of each ally listed, though I understand you can find each of them fully described in Dragon Heist. Perhaps that was the intent, it just wasn't clear to me when I bought it.

That said, this is a well written, well edited and well structured adventure with interesting concepts and mechanics, so I'd still recommend it for those with a little more knowledge about the setting than me.
Customer avatar
James I November 19, 2018 1:31 pm UTC
Hey Luciella! Thanks for the feedback. Like all Adepts products, this one is meant to support current Wizards of the Coast releases like Dragon Heist and DotMM, which is why this product's first chapter is intertwined with those products. That said, while playtesting it was definitely possible to run the adventure without having run or read those products, but it does require a little work on the part of the DM to either research (a lot of which can be done through Google) or tweaking the story of the adventure while keeping the mechanics the same.
Customer avatar
Brian P April 02, 2020 4:01 pm UTC
I'm going to run this Sunday (and expect to take two sessions), I'll review after. But I'm running it for a group that has never seen Waterdeep. (They did a largely Chult-based campaign with these level 20 characters.)

I would agree that running this as a one-shot for a group unfamiliar with Waterdeep will be tougher. Although most of it will require little change, the "Mustering Defenses" section will have to be rewritten or largely improvised for most groups. Which it probably would anyway, based on a group's experiences in Waterdeep and their history with the factions mentioned... My plans are to collaboratively improvise that content based on whatever wild ideas the players come up with. If you have a group that actually made their way to level 20, chances are good that they have picked up a number of weird allies (and enemies-with-common-interests) along the way, and you'd probably have to deal with some off-the-rails ideas anyway. I see this section as mostly roleplay, but there are...See more
Customer avatar
Brian P May 04, 2020 1:05 pm UTC
Now that I've run this (will review), I'll return to what I said: I think this adventure provides a good framework to run this in any big city that you (and the players) are familiar with; but it'll fall flat if you roll a group just for this adventure. The early section revolves around mustering allies, and I thought those were easily improvised with different campaign-appropriate allies. But, without old friends (or enemies (or frenemies)) to revisit, most players will find that section of the adventure either directionless or lacking emotional resonance.
Customer avatar
Fynn H November 10, 2018 10:13 pm UTC
Is this likely to become AL-legal? I want to finish off my AL HC with this! :)
Customer avatar
James I November 12, 2018 1:16 pm UTC
I don't think this one is likely to become AL legal. It's a little too ridiculous and over-the-top. I will let you know if that changes though!
Customer avatar
Paul H August 26, 2019 7:34 pm UTC
Considering how crazy the rest of the DMM and modules are, I actually thought this was a great finisher to that storyline. I'm hoping this gets added to the approved by AL list.
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File Last Updated:
January 29, 2022
This title was added to our catalog on November 09, 2018.