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Yes. Potions use an NBT "Potion" tag to indicate the potion type. http://minecraft.gamepedia.com/Potion#Data_values

Item.getItemFromBlock(Block) will return the ItemBlock instance of the Block.

Comp-sci for the curious: Each block position in the world gets a 2-byte (16-bit) integer to tell what it is. 4 bits are the metadata, and 12 bits are the ID. That gives you the ranges 0-15 for metadata and 0-4095 for block ID within which we must work. I 2nd the motion to use metadata wherever you create sets of blocks by color or wood or any other simple parameter. Otherwise those bits go to waste.

The fields at the top of the GameData class hold the minimum and maximum IDs for the vanilla registries, i.e. Blocks, Items, Potions, Biomes, SoundEvents, PotionTypes, Enchantments and Entities.

IIRC, 4096 for Blocks and, ~32000 for Items.

If the chat GUI is already open, you can add text to it by calling GuiTextField#writeText on GuiChat#inputField. The field is protected, so you'll need to access it via reflection.

See if you can find the source for the Morph Mod

There's a whole tangle of code associated with being a player, so I think you're going to need to go with an extension of EntityPlayer. That means try the substitution(s) and re-skin.

World#getBlockMetadata returned the block metadata at the specified position, World#setBlockMetadata set the block metadata at the specified position. Metadata was replaced by the block state system, you can read an introduction to it here. Use World#getBlockState and World#setBlockState instead of World#getBlock/World#getBlockMetadata and World#setBlock/World#setBlockMetadata. Use IBlockState#getValue to get the value of an IProperty in an IBlockState and IBlockState#withProperty to get an IBlockState with the IProperty set to specified value. I would recommend against updating to 1.8, since it's outdated and not really supported by Forge any more. I recommend updating straight to 1.11.2, or at least to 1.8.9 if you have to use a 1.8.x version.

Where did you register the renderer?