Using WorldEdit with blocks added by mods (modded blocks) on Minecraft versions before 1.13 can be confusing. The ID from the inventory doesn't work, and you can't use the block's name. Due to the way Forge works, the ID you see in the inventory isn't actually the block's ID, but there are a few different ways to set blocks from mods easily.
On modern versions of Minecraft, blocks use namespaced IDs, such as minecraft:grass_block. This system makes it much easier to use modded blocks with WorldEdit, but versions earlier than 1.13 lacked this. Therefore, it takes a little more effort to find the actual ID.
Using the Info Tool
The simplest way to get the actual ID of a block added by a mod is to use WorldEdit's info tool. To use the info tool, do the following:
- Place the block you want to set
- Hold any item in your hand (not a block)
- Run the
/infocommand - Right-click the block you placed with the item
- The chat will have a message that has both the #id and [data] values
- If it says #991 and [5], the block's ID is 991:5
- Use that ID in the WorldEdit command
Using the /info tool
Using the clipboard pattern
Sometimes mod blocks have extra data that they require to work. Using the ID isn't good enough in these cases, but there are ways to use the block still.
WorldEdit accepts #clipboard in place of a block ID, allowing you to //copy something and then use that block. This feature is called the Clipboard Pattern.
While intended for setting intricate patterns or structures, this system also works to set mod blocks containing extra data.
To do this, select the block you want to use with the selection wand and run //copy. Then you can use #clipboard in place of block IDs in practically any WorldEdit command.
Using the clipboard pattern
Notes
Do note that if you're running a hybrid server that allows both Bukkit plugins and Forge mods, it's necessary to install both the WorldEdit mod and plugin. Hybrid servers can often cause other issues, though, and are generally not recommended.