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With the Wrath of the Lamb expansion, The Binding of Isaac now has two different kinds of secret rooms, and together they seem to have somewhat complex placement rules.

If I can only search for these rooms with bombs by blowing up one side of a room at a time (the usual case), is there some search pattern that will minimize the expected number of bombs needed to find both rooms or maximize the expected number of rooms I find with a limited number of bombs? In other words, in general, is there any order in which I can try bombing walls that puts the most likely walls first?

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The old secret rooms can be found in the same way as before (gaming.stackexchange.com/questions/45530/…) while the new ones (the secreter rooms) never show up on the map until you've been in them, and only need to border 1 other room, so I'm pretty sure there's no way to reliably find them with few bombs. –  Mr Smooth Jun 12 '12 at 4:02

3 Answers 3

Ok, let's try to answer this with the use of images.

But first, a little explanation. It is known from experimental evidence (and reported also on the wiki) that the Secret Rooms (the old ones, SR from now on) and the Top Secret rooms (TSR) have the following behavior: SRs are usually surrounded by 3 or 4 other rooms, while TSRs are usually found with a single room near them. There are exceptions, but we'll se them later. Also, based on my experience, a TSR is never found near other special rooms. Finally, EVERY level has both a SR and a TSR.

Now, to answer your question: which walls should you bomb to have higher chances of finding a secret room? Let's see some examples:

  • Example 1.1

The first case is straightforward: we know that a SR has 3 or 4 other rooms around, and there's only one spot in the map like that. Bombing one of the red walls will bring you to the SR. For the TSR it's simple as well: while all the yellow-highlighted walls could bring you to a room that has no other rooms connected, they all belong to special rooms, so that leaves the green wall. So, in this case, with just two bombs you get both treasure rooms, as you can see in the following image: Example 1.2

  • Example2.1

This one's trickier. While searching for a SR, you'll see that you have three spots that qualify, the two walls in purple and the one highlighted in red. In this case there's no way to tell which one is the real one, so you can waste up to three bombs while searching for the SR(the purple walls were the wrong choice, by the way). For the TSR it's even worse: any one of the yellow walls could be a possible choice, and each one of them would make you waste a bomb, because the green wall hides the actual secret room. The only thing that can help you here is your luck, unless you have a huge reserve of bombs, the X-ray glasses, or the Spelunker Hat when McMillen manages to fix it (it's currently broken and doesn't do anything).

  • Example 3.1

This may be the trickiest case, at least the first 4 or 5(hundred) times you get it. Strong of your previous experiences, you may think that the purple walls are your best bet for a SR, and the yellow for the TSR. Sadly for you, this is the exception I was talking about earlier: the TSR can be generated with two rooms around it if one of those is a SR. Adding insult to injury, the TSR will count as the third room around the SR. Always keep a handful of bombs ready for these situations, and remember that both of the secret rooms are ALWAYS present in every level.

As you have seen, with both kinds of secret rooms, you always have to make some guesses, so having enough bombs(or Ipecac, or Dr. Fetus, or Epic Fetus) surely helps. Anyway, you can always narrow the possibilities by paying attention to the layout of the level. Also, the DLC brought a whole lot of highly dangerous new enemies that explode or shoot explosive bullets. Use them to your advantage, and lure them near the walls you want to blow up; saving bombs is always a good thing!

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This is interesting, but not exactly what I was looking for. I was trying to ask whether there was an order I should bomb walls in, preferrably backed up by some math if possible. –  murgatroid99 Jun 12 '12 at 10:54
    
@murgatroid99 you can't actually do "some math", since it's a random generated dungeon. You can prioritize though, choosing to check the potential rooms with 3 or 4 surrounding walls (or just one if you're checking for the new ones). I'll try to put this in the answer later, with a better explanation. –  Kappei Jun 12 '12 at 11:02
    
The fact that this is a random process just means that any math will be probability theory, not that math doesn't apply. And even though the map is different every time, it might be possible to have a general answer from which one would be able to figure out what walls to bomb first given a floor map. –  murgatroid99 Jun 12 '12 at 13:42
    
@murgatroid99 ok, I get what you meant. I'll rewrite my answer as soon as I can, trying to use some more SCIENCE! –  Kappei Jun 12 '12 at 13:56
    
Great! I would do it myself if I wasn't at work. –  murgatroid99 Jun 12 '12 at 13:56

For me, it really comes down to experience, and just a tad amount of luck. Now, finding secret rooms is relatively easy. You usually focus on the empty spaces with a lot of adjacent rooms.

There are of course, those times where it seems like there simply isn't a place for the secret room i.e., you've exhausted all of the spots with 3 adjacent rooms, or there simply were none to begin with.

My guess for these types of floors, is that the Super Secret room must be the third room. Either this, or instead, the Secret room is only connected to 2 rooms. I'd however not attempt these types if I thought that the second were true.

If you're going to attempt to find the secret rooms on that floor believing that the first of the 2 ideas above, be mindful about whether the super secret room could indeed fill in any of the potential third slots.

On another note, if a Curse Room is adjacent to a secret room of any type, then a spiky doorway frame will connect the two.

Now, there are some things you can do to help as well. Try to trick your foes into doing the dirty work for you!

Note that the efficiency of this depends not only on your skill in dodging, weaving, and avoiding danger, but also on your level of patience.

If the enemies in the room always aim explosive shots at you, stand near the walls, and quickly move out of the way just before they shoot them. Repeat for all of the other walls if unsatisfied.

If any enemies in the room randomly shoot explosive shots with no regards as to who or what they hit, and are able to move (Walking Guts are an example, they're green versions of Boils), simply wait it out until A. You're certain that they had accurately hit the wall... or B. You no longer feel safe and comfortable prolonging this. The amount of explosive potential enemies you leave alive is determined by your level of comfort, but do try to limit their numbers to at least 3...

Lastly, you have Bomb Flies, Mulligoons, and to a lesser extent, Mullibooms. Simply wait until they approach a wall, and attempt to time their death so that they die and explode on the wall. A bomb fly can fly near any potential doorway given enough time, so be extra patient with this method. Mulligoons when killed, drop a Troll bomb, so if you're daring and quick enough, you can push this into a wall, if it might not seem close enough.

Then there are those Mullibooms... I however, have not intentionally led these types of enemies in the hopes of uncovering a secret room. I find that their pursuing nature, and instant explosions makes them a dangerous choice for this sort of action.

This is just about all I can suggest. I will remind you however, that this all really does come down to simple experience. The more you do this sort of thing, the more likely you'll accurately guess the location of any of the secret rooms. Consider this one important thing though... Never ever try to actively bomb open a secret room of any type if you do not have a great deal of bombs. Taking a guess now and again is ok, but don't waste 3 bombs if you only had 3 to begin with.

Understand that basic secret rooms, which are known for (but not limited to) carrying large amount of money), lose value once you enter the Womb, simply because A. All currency loses value starting from the Womb, and B. Because the most common drop in Secret Rooms is money.

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The most efficient way is to use the x-ray glasses which are in the game.

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Thanks. While it is true that x-ray glasses are the easiest way to find secret rooms, this is not what I was looking for. I can't count on finding the glasses, and I specifically said "If I can only search for these rooms with bombs" –  murgatroid99 Aug 5 '12 at 22:00
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This is really a comment, not an answer to the question. You can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. –  kalina Aug 16 '12 at 9:51

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