ALL MONSTER PATTERNS (spoilers)
-The Dragon always spawns in the middle column fifth row from the top
-The Dragon Egg is always adjacent to the Dragon orthogonally or diagonally
-The Wizard is always on the edge of the map surrounded by five purple slimes. It is possible for one of those slimes to spawn in the corner of the map.
-The lovers Romeo and Juliet spawn in the same row "mirrored" along the middle column. They can also spawn in corners.
-Why talk about corners so much though? Well, the Mine King always spawns in a random corner of the map, and determining which of the four corners has him is very important in 365/most health runs.
-Each of the four Guardians (7 health enemies) spawns in a region of the map divided by the Dragon's row and column. Therefore, Guardians cannot spawn in the Dragon's row and column and no two Guardians can appear in the same "sector" of the map.
-All Minotaurs and Chests on the map are adjacent to each other. This pattern can be helpful in finding the Mimic, although the Mimic can spawn adjacent to Minotaurs along with their Chests.
-Gargoyles and Walls spawn in orthogonally-adjacent pairs. Gargoyles in pairs will also face towards one another. The pairs of Gargoyles can be adjacent to one another while the walls cannot.
-If a Rat is in the same column as the Rat King, it will be sitting. Otherwise it will be standing and will "face" toward the column where the Rat King resides.
-To find the Gnome, the player must simply uncover every blank tile on the map.
-The beginning tile with the blue orb or whatever it's called cannot spawn in the outer two rows/columns of the map such that it will always reveal its full area when interacting with it.
-On the other hand, the acroll that reveals a random 3x3 area on the map can reveal an area centered on the map's edge, making it less useful.
-Everything else is random bullcrap go
Feel free to correct me in the comments or add additional information. Hope this is helpful!