Ring of Pain

After win a run you will unlock the Double Candle which is the most optimal item for the achievement runs.

Start a run with Hermit's Tiara and try to find Misting Vessel and a weapon with speed in the first floor. The achievement itself it's luck based, since you need to grind a lot of souls to reroll golden chests until you get a Polearm, after that, pray the RNG gods for a Chills floor to appear, here is the Ancient Ice Beast, just poke it with the polearm (move left and right) until the monster die.

The other guide on this page is good for a guaranteed kill, but the RNG of finding both the legendary weapon you need and the path to Chills is so absurdly small that I thought I'd share a few of my findings in order to increase consistency so that you're ready when Chills is open

To get this achievement, you must find an Ancient Ice Beast within a Chills optional room. On normal difficulty, Ancient Ice Beast starts with 12 defense, so in order to raise its defense to 30, you must inflict the freeze status on it, which will negate the freeze and instead raise its attack and defense by five points

As mentioned in the other guide, the best way to start out is to unlock Double Candle (unlocked by clearing normal difficulty on light ending) and equipping Hermit's Tiara. This will not only be your primary freeze option, but will also help you roll most floors without taking too much damage

Your goal from here is simple - chase down as many stat boost cards as possible, and do as much soul farming as you can in order to ensure you have as many opportunities for win condition items in the epic (purple) and legendary (gold) categories

Since Hermit's Tiara is only effective if you have four or fewer items equipped (with the candle counting as an item), it is NOT recommended you pick up any common (gray) or rare (blue) equipment, as none of them were useful for this achievement, from my experience. If you find a Wishful entrance, you can collect a few items to toss into the shrine, but generally, do not pick up any commons or rares you don't think you can easily get rid of

That said, there is one exception to this rule - scrolls. If you find scrolls, they are easy to use once and dispose of, so you can pick those up and use those without breaking Hermit's Tiara. There is one scroll in particular that you're looking for, and that is Soul Spill. This is a powerful common scroll that will allow you to instantly kill the Ancient Ice Beast if you can get its defense up to 30 and you have a lot of souls stockpiled. Once you get this scroll, it's recommended that you hold on to it for as long as possible and do not replace it with another scroll

For stat cards, be sure to chase down every Scrounger you can find for its potions and stat boosts. Since you're not aiming to clear the dungeon, it's recommended that you add stats to defense and health as often as possible so that you can eventually parry the Ancient Ice Beast repeatedly until it reaches 30 defense

So that's the basics of what you should start with in every attempt. Now for the fun part - the gear you're looking to equip that will help make this job a lot easier. I'll give a quick blurb to each piece of gear that's relevant to taking down Ancient Ice Beast, some of which are epics and some are legendries. Keep in mind that you should only pick up one of these pieces of gear per run, since if you have a piece of gear and Soul Spill and equip another piece, Hermit's Tiara will stop inflicting freeze

Glacier (Epic) - Must be paired with Soul Spill and a high defense. It'll allow you to inflict freeze on Ancient Ice Beast twice in one turn if you parry the hit (which can be up to an 80% chance). This will allow you to get Ancient Ice Beast's defense up to 30 in fewer turns and unleash Soul Spill on it once 30 has been reached

Icy Touch (Epic) - Must be paired with Soul Spill and zero or less attack. It'll allow you to inflict freeze on Ancient Ice Beast without attacking it, allowing you to safely get its defense up to 30 without risking damage. Note that it takes five attacks to recharge, so once you use it, you should farm other monsters in the room for one damage each before using the spell again, hence why zero attack is recommended

Dual Wield (Legendary) - Soul Spill recommended but possibly not necessary if you have decent attack. This gear allows you to attack both front enemies at once, so position yourself in between two enemies and simply attack the one that isn't Ancient Ice Beast. It will receive the freeze effect without attacking you, making this a safer option to deal damage

Freezing Aura (Legendary) - Must be paired with Soul Spill with a high defense recommended. Similar to Glacier, but freeze occurs when you are hit instead of when you parry. Generally it's a safer option to increase its defense when you are hit instead of relying on the parry, especially when Ancient Ice Beast ignores parry once its attack is high enough

Polearm (Legendary) - No other requirements. Obtaining this item allows you to attack Ancient Ice Beast simply by passing towards it, allowing you to move back and forth and deal at least one damage while inflicting freeze every other turn. Since you don't need Soul Spill, you can include one other item for stat purposes, but generally this is your win condition if you can obtain it

Backpack (Legendary) - No other requirements. Though this doesn't directly help you freeze Ancient Ice Beast, it indirectly unlocks the rest of your inventory by allowing Hermit's Tiara to always work no matter how many items you have equipped. This is extremely useful in terms of simply surviving while increasing its defense. Just make sure you don't equip something that kills it too quickly!

Frost Root (Legendary) - Must be paired with Soul Spill and a high defense. Pretty much just a safer option than Icy Touch as it only takes three attacks to recharge instead of five. Gives you more opportunities to farm recharge against other enemies in the room

As a note, Ancient Ice Beast doesn't actually freeze when it is inflicted by it, so any items with language that benefit against frozen creatures won't be helpful against it

Once you have one of these win conditions above, you are good to fully hunt for Chills. It has a chance to spawn as an alternate entrance in numbered rooms, but from my experience I had a much better time finding it by going through Pathways, which guarantees you two or three optional rooms. The usual problem I had is that by the time I had one of these win condition pieces of gear, it was already floor 10 or 11, so there weren't many more opportunities to randomly get the correct room

For full transparency, my successful win condition was with Backpack, which allowed me to grab as many pieces of gear as possible and increase my damage in time to poison Ancient Ice Beast to death after getting to 30 defense. Best of Luck!