Minecraft – Entity lighting bug or invisible entity parts or just like that

Unique Item

• Dragon Egg - only obtainable by killing the Ender Dragon.

Rare Items

• Saddles - Only found in chests in dungeons, Nether Fortresses, Desert and Jungle Temples, and NPC villages. Can also be obtained by trading with Villagers and fishing. It can also be obtained by killing a ravager.
• Horse Armor - Only found in dungeons, Nether Fortresses, Desert/Jungle temples, and NPC villages.
• Music Disc - Only gained by tricking skeleton into shooting a creeper with its arrow. Also, discs "13" and "cat" are found in 8% of dungeon chests.
• Name Tag - Only found in chests in dungeons, Nether Fortresses, Desert and Jungle Temples, and NPC villages. Can also be obtained by trading with Villagers and fishing.
• Melon Seeds - Can be found in minecart with chests in abandoned mine shafts. You can also get them from NPCs.

Rare Mob Drops

• Ender Pearls - A rare drop from a rare mob (Endermen).
• Blaze Rods - Blaze are flying mobs in the nether; hazardous to kill. Can be used to make a few other ingredients via Blaze Powder
• Ghast Tear - Prone to falling into lava when you kill the Ghast.
• Wither Skeleton Skull - A rare drop from a somewhat rare mob (Wither Skeleton).
• Nether Star - An item drop from the Wither Boss
• Mob head(other than Wither Skeleton) - Can only be obtained by blowing up the said mob with a charged creeper (creeper struck by lightning).

Rare Blocks

• Emerald Ore - A new block that only generates in one biome, and generates between three and eight blocks per chunk. Used as a currency for trading with NPC villagers.
• Beacon Block - An item crafted from the Nether Star, 3 Obsidian, and 5 Glass.
• Sponge - Found only in ocean monuments and dropped by Elder Guardians.
• Ice - can only be mined with a silk touch pickaxe, can only be made in a snowy biome.
• Packed Ice - A more compact version of Ice, but doesn't melt in Torch/Glowstone light, only found in the rare Ice Plains Spikes biome, and obtainable only with silk touch enchanted Pickaxes.
• Prismarine - Only found in Ocean Monuments. It can be crafted from prismarine shards dropped by Guardians.
• Sea Lantern - Only found in Ocean Monuments. It can be crafted from prismarine shards and prismarine crystals dropped by Guardians.

Other

• Bedrock/Adminium - Cannot be mined, found at bottom of map or top of the Nether. Must be spawned through the console to place.
• End portal and End Portal Frame - 1,152 end portal blocks per world and 1,536 end portal frame blocks. (As of 1.15)
• Command Block - Only obtainable via console command.
  • Command Cart - Also must be obtained by commands.
• Barrier - Obtained by commands.

Update: According to Notch's blog post about changes coming in 1.6, the torches-on-fast-leaves bug is getting fixed:

• Fixed buttons and levers being placeable on leaves in “fast graphics” mode

This means that monsters can no longer spawn on leaves, either, as they are always considered transparent, even when using Fast graphics.

Monsters can spawn on any solid, non-transparent block which is at light level 7 or lower.

Signs, torches, rails, and the like are ignored when spawning monsters; they'll spawn on the block underneath just fine. This is why one-block-wide railways need to be lit.

Transparency means whether or not light passes through a block rather than whether you can see through it. Half-blocks, doors, stairs, and glass all count as transparent and prevent monster spawning. Leaves, oddly, count as transparent only when Fancy graphics are enabled. An easy way to test a block for transparency is to try placing a torch or sign on it — neither can be placed on transparent blocks. (Meaning that torches can be placed on leaves with Fast graphics, but not with Fancy.)

Torches put out light level 14, so monsters can't spawn within 5 blocks of a torch orthogonally or 3 blocks diagonally. If you put your torches in a diamond pattern, they can be up to 9 blocks apart, but it's best to move them closer than that on uneven terrain. (I use 5 myself.)

If you like, you can actually torch your treetops by changing your graphics to Fast, placing the torches, and switching back. Your torches will stay rooted, even though you wouldn't normally be able to place them that way. Personally, I think it makes them look rather cheerful. :-)