"Double Rainbow" achievement guide

How to build a character that inflicts all special damage types with one attack, in order to gain the rare "Double Rainbow" achievement.

Objective

This achievement requires you to inflict every special damage type and one mundane damage type with a single attack.
"Special damage" is everything that ignores your opponent's armour: Piercing, conflagratory, hyperborean, voltaic, toxic, acidic, putrefying, asphyxiative, necromantic, righteous, aethereal, transmutative, existential damage.
Note that this does include piercing damage (a common weapon type), while blasting damage (a fairly uncommon element) and the more mundane crushing and slashing types are not required.

Your status screen should look like this in the end

This guide relies on weapon encrusting, archaeology and buffs to inflict all these damage types with a melee attack.

You will find a lot of equipment with elemental damage on it, but which elements you get is unreliable.
This guide is meant to make up for that swing by giving you access to many elements via crusts, buffs and potions, so you can hopefully get the achievement in any run. If you're still missing a rare element, archaeology is there for you.

Gathering the necessary ingredients is a lot more effort than a normal run and dangerous instabilities may ruin your precious weapon, so I highly recommend playing without permadeath for this achievement run.

Core skills & damage sources

Core

• Archaeology helps immensely with this achievement, because "This Translation Is All Wrong" lets you reroll enchantments on your gear, and "Ancient Kronian Ritual" resets anvils so you can get more enchantments.
  
• Alchemy and smithing allow you to make crusts for a whopping nine elements, including rare ones like existential, acidic and putrefying:
  
• Smithing lets you make existential, voltaic, conflagratory and hyperborean crusts, plus several elemental weapons from recipes.
  
• Alchemy grants toxic, necromantic, acidic and putrefying crusts, righteous damage via potions of radiance, and transmutative or aethereal damage via staves.

Options

• Astrology grants righteous and ethereal damage on demand.
  
• Fungal Arts drops Fell Truffles for necromantic and putrefying damage.
  
• Demonology grants righteous and conflagratory damage.
  
• Piracy will get you all the (alchemically transmutable) gems you'll ever need.
  
• Paranormal Investigator grants loot and crafting recipes and transmutes potions.
  
• Dual Wielding can be handy as a second enchanted weapon usually has more different damage types on it than a book or shield.
  
• Viking Wizardry gives voltaic+hyperborean damage on demand, but these are among the more common elements.

Piercing damage is ubiquitous, you shouldn't need to take any precautions to get it. If your enchantd weapon isn't piercing, you need pointy boots or something.
Asphyxiative damage is a tricky one. There's no crust nor buff for it, and it'll likely be the last type you're missing at the end. At that point, spam This Translation Is All Wrong! on your weapon or a ring and hope for the best.

Thanks to archaeology, altars, potions and common items like the Cybertronic Amulet or Pyromancer's Gauntlets, you're likely to get a few elements without encrusting. Having to make less crusts is good for your patience and your crust stability.

Survival

Getting all these crusts, artefacts and crafting skill levels takes a bit of time, almost as much as getting to the bottom in a normal run. I'm not covering survival strategies in detail here, but giving some suggestions.

This build suggests encrusting a melee weapon because ranged builds require much more specialization to be effective, while melee characters can sort of get away with having a topsy turvy build.
For this reason, I recommend either a physical fighter setup or a gish mage one.

For weapon skills, I either suggest something with piercing damage, or staves to support a crafted transmutative staff. If you max staves it will also grant aethereal damage.

The core skills of this build offer you encrusted weapons (smithing/alchemy, covered above), armour (smithing), healing (alchemy) and trap affinity (archaeology+smithing).
One thing they lack is a consistent zoo clearer - you can use alchemy to make brimstone flasks, and it's awesome, but you probably won't have enough. Because you need levels of Alchemy anyway, Rogue Scientist can remedy that. (A silly, but slow and hardly viable alternative is to take Werediggle, lay eggs and make brimstone flasks out of those)
Other things you'll need are obviously survivability and either warrior or gish mage skills for damage. Which one, is a matter of taste.

Gish mage options

• Staves are a good weapon choice, see above.
  
• If you have astrology, you probably can't spare the points to unlock its big damage spell. The stuns will still be a lot of help, especially in combination with those from the Staves weapon skill.
  
• Necronomiconomics probably requires too much specialization as well. That said, if you can make it work, it always works extremely well.
  
• Warlockery is already nice at the early ranks - Mage's Mana Maille gives huge defense for a level 2 skill. (Alchemy can feed it.) Note that Puissant Touch's aethereal damage doesn't count as part of your weapon attack.
  
• Promethean Magic can decimate zoos even at skill level 1 or 2, but requires tedious spamming and is useless against fire-resistant enemies. But if you want a mage with a pet, it probably fits better than Golemancy.
  
• Viking Wizardry is mostly redundant because your melee attacks should be enough for single-target damage, and you get its elements from crusts. But Unholy Warcry is overpowered, and makes this always an option.

Fleshsmithing's healing/defense are probably unnecessary, and its area damage requires too many skill points and is nearly useless later on.
Don't take Wand Lore solely for aethereal damage, Astrology fits the bill much better. If you like wands though, go ahead.
Hands off Egyptian Magic, it requires too much specialization.
That said, it might be possible to focus on Egyptian Magic until you can wreck everything, then easily powerlevel to get the crafting skills for your super-elemental weapon.

Warrior/rogue

• Weapons are a matter of taste. I don't recommend Axes for this because you want piercing damage.
  
• Aside from the accuracy, vision and healing, Big Game Hunter offers tons of lutefisk. Once you have enough healing potions, you can grind up all the spare meat, transmute it to lutefisk and get one or two extra big sacrifice rewards from the Lutefisk God.
  
• Battle Geology can carry you through the early ranks and offers lots of defense and a low-cooldown stun/ranged attack. Lovely.
  
• Shield Bearer or Master of Arms is a matter of taste. The latter's advantage is that you get the big regen buff at level 2. If you can max it out somehow, Shield Bearer is better at the end because it gives more utility. Master of Arms's procs are effective if you deliberately tank hits, which you can't really do with this build.
  
• Fungal Arts is nice if you like pets and potions, because that's what it gives you.
  
• Piracy synergizes with alchemy for gems. Swashbuckling is great but not good enough to be your only source of melee defense, because of its cooldown. Mists of the Corsair is redundant with archaeology, so there's not much of a point in levelling it higher. The cannon is also good for lutefisk though.
  
• Communist offers good stealth and healing, but that's all you should expect. With their drawbacks and focus on crafting, the high-level skills require too much specialization, and you don't have many skill points to spare anyway.

Berserker Rage requires more defensive skills, and there's a bug that makes its level 4 skill sometimes drain stats permanently.

Stuff that generates items, like Fruitful Staves, Big Game Hunter's Butchery or piracy's cannon have the additional advantage of giving you stuff to turn into lutefisk and sacrifice for more artefacts.

Execution

You'll have to focus on surviving in the first place early on - this build is a little bit topsy-turvy. Take a few points in the survival/damage skills of your choice.
For pure survival, smithing generally helps the most among the core skills. An early point in "It belongs in a museum!" is also always good.
If you find the ingredients for a weapon you want to build, get the crafting skill for that.
It's pretty much business as usual at this point - scavenge, fight stuff using weapons, items, spells, skills, pets, whatever you may be using - except for the fact that you should get familiar with your crust recipes and put any of their ingredients you may find aside.

Now for your "super weapon".
I highly recommend using an artifact weapon for this purpose. You'll likely find a few high-tier recipes with some elements on them. Obviously, choose a weapon with many elements that aren't covered by your skills.
I like staves because many of them have uncommon elements - for example, transmutative damage is hard to come by otherwise, but a common attribute of staves.
I suggest not doing any encrusting before floor 6, or whenever you can make 80% of the crusts you need, unless you know for sure that you have the weapon you want to work with.
You may find something much better, especially in an Evil Chest, and lucky enchantments may make certain crusts unnecessary.
Whether to use a weapon from an Evil or Holy chest, depends on what's covered by your skills. Holy weapons' elements are redundant with Astrology and Staves, for examples.
Save before you encrust, if you're playing without permadeath; encrusting may cause ruinous instabilities.
For the same reason, I recommend applying every crust only once; repeated crusts are especially prone to instability.
If you're still missing an element after the big encrusting session (likely asphyxiative), it's time to grab an accessory with many enchantments and spam "This Translation Is All Wrong!" on it, and reset the skill with Magical Law or just fast forward and walk back and during the downtime.

Once you've got your rainbow loadout, you need to find a monster that can't nullify any of your damage types through resistances. The easiest method is to go all the way back upstairs and smack a poor diggle on the head.


This attempt was missing piercing damage, but I was nearly there.

Good luck!

[Syn]

After probably 8 or so years, I finally got it thanks to this guide. Thank you so much!

[House of Eats, Shoots and Leaves]

No problem! I wrote most of this down to get this achievement myself, and I thought I might as well share the notes so it's easier for others.

[Great Azatot]

Thanks for the guide man!