Planetarium

简介

The Planetarium is an unlockable room type added in The Binding of Isaac: Repentance. Planetariums are similar to Treasure Rooms, in that they both require keys to enter, but always contain special astronomy-themed items that are only available through Planetariums. Their chance for appearing increases with each Treasure Room skipped. They are unlocked by acquiring three different astrology-related items in a single run.

Generation Chance

Planetariums can only appear in chapters 1, 2, and 3 (Including their alternative floors). * allows Planetariums to generate in Womb and Corpse. * However, Planetariums can appear in the additional Mausoleum II / Gehenna II level that is accessed through . The base chance for a Planetarium to generate is 1%. This chance can be modified in various ways: In other words, every Treasure Room skipped will add 20% to the generation chance. However, if additional Treasure Rooms are entered, such as those created by Forget Me Now or Red Key, then the 20% penalty for entering a Treasure Room will be taken without receiving the 20% bonus for descending a floor. * The combined percentage from descending floors and entering Treasure Rooms will never go below 0%.

Notes

* 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. Holding both of them with Schoolbag doesn't count either. * If Isaac loses passive items (ie: using the D4) they will not count towards the unlock. In other words, Isaac must have 3 items simultaneously. * Planetarium items can be found before Planetariums have been unlocked in-game. To do so, use any method that ignores item pools (Chaos, Eden, etc.). * If attempting to find a Planetarium to obtain one of its items, very careful consideration should be taken before picking up Rosary, as this will add The Bible to the Planetarium's item pool. Given the pool's small size, you will have a high chance to find it instead of a normal Planetarium item.

General Strategy

Overall, the Planetarium items are average to above-average. None of them are bad, but none of them are particularly gamebreaking either. So, given that skipping a treasure room doesn't guarantee a Planetarium showing up, it usually isn't worth skipping Treasure Rooms without a good reason to do so unless you're doing speedruns. In speedruns the global strategy is to skip everything to go to the last floor. So in that case, Terra and Mercurius are the best items and overall skipping Treasure rooms is always worth since we can have a build with only Devil or Angel deals. Given the Ascent path takes Isaac back through previous floors, it is viable to skip item rooms on the way down to improve his chances of the Planetarium spawning and then getting the items from the rooms he skipped on the way back up. However, Planetariums can NOT generate during the Ascent, nor will skipped Planetariums "reappear".

Statistics

Without , Planetarium rooms can't be found in chapter 4 and after. Since the chance to find a Planetarium depends on the number of Treasure Rooms skipped, skipping earlier ones allows for a higher cumulative chance of encountering one. The table below presents the chances if the first Treasure Rooms are skipped. For example, if the first two are passed on, there is an 84% chance to find a Planetarium between Basement I and Depths I.

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