The easiest way i found to unlock the Planetarium (The stars are calling…) [Repentance DLC]

Overview

Why just rely on luck when you can craft your way to the stars?In this guide I’ll show what i have done to unlock the achievement “The Planetarium” and its astronomical room.Stay aware that this obviously have heavy spoilers on the content of the DLCs. If you don’t want any spoilers, this is your last oportunity to leave.

Unlockings needed

For this method you will need to unlock the following:

• Cain
• The Polaroid, The Negative or Faded Polaroid
• Polaroid Door on Depths
• Red Key or Cracked Key
• Faded Cain
• Lucky Penny, Rotten Heart (not obrigatory)

Unlocking the needed character

The character i used to unlock the Planetarium wasFaded Cain, which is unlockedby giving the polaroid door one of the following: The Polaroid, The Negative or Faded Polaroid. The most common way is going to Depths II (the floor that you fight Mom), bomb one tinted skull to obtain 0 – The Fool, fight Mom and kill her, get one of the polaroids, use 0 – The Fool to go back to the start of the floor. When the door is open, you can make your way back to Home. If you already unlocked Red Key by opening Mom’s chest, you must drop a trinket on a boss or treasure room before picking up Dad’s Note. Back at Home, on the corridor before Mom’s room, use Red Key/Cracked Key to unlock a secret door, where you unlock the Tainted version of your character; in this case, Cain.

When you have made all the steps above,go to the character selection and press E. That will display another crowd of characters, named Tainted characters. ChooseTainted Cain and you are halfway done.Tainted Cain have a special trait. All pedestal itens he touches turn into a bunch of consumables, but he can collect 8 of them and with a specific combination, make a item. Each item has some combinations attached to it. More on that later.

The method

According to the wiki[bindingofisaacrebirth.fandom.com], the quote says:

Originally posted by The Binding of Isaac Rebirth Wiki:

Planetariums are unlocked by acquiring three different astrology-related items in a single run. These items include the Signs of the Zodiac, Magic 8 Ball, Crystal Ball, and Star of Bethlehem. The Crystal Ball will not count towards the unlock if it is left behind after picking it up. Note that the item Zodiac does not count.

Patch v4.0.3 edit:

• New items were added on the pool. These items are Card Reading, Deck of Cards, Echo Chamber, Tarot Cloth and Zodiac.
• New quote from the wiki[bindingofisaacrebirth.fandom.com]:
  

  Originally posted by The Binding of Isaac Rebirth Wiki:

  Planetariums are unlocked by acquiring three different astrology-related items in a single run.

  These items include the Signs of the Zodiac, Card Reading, Crystal Ball, Deck of Cards, Echo Chamber, Magic 8 Ball, Tarot Cloth, Star of Bethlehem and Zodiac.

  The Crystal Ball and Deck of Cards will not count towards the unlock if they are left behind after picking them up, they must be actively held.

I made (in order): Scorpio, Magic 8 Ball, Tiny Planet and Aries. It’s worth noting that Tiny Planet doesn’t count to the unlock.

In order to craft items, you need theBag of Crafting, item whichTainted Cain comes with. Here is a preview of the item.

Craftings

There are the craftings of the items i took from Isaac Cheat Sheet[platinumgod.co.uk]. Crystal Ball is missing because it is uncraftable (see below).

Patch v4.0.3 edit:
New items were added, here are their craftings:

Crystal Ball is an uncraftable item, as listed below: