Command Reference

//wandPuts a wooden axe in your hand which you can use to make selections. Make selection by right clicking on one corner and left clicking on the opposite corner
//drawselThis toggles on/off the ability to see a glowing outline around the blocks you selected.
//pos1 and //pos2When there’s no block to click on to make a selection, you can hover in the spot you want to select and type //pos1 for the first corner and //pos2 for the opposite corner
//set [block-type]Once you’ve made a selection, you can type this followed by the block you want, and it will fill in your selection with that block.
Example:
//set red_wool  

You can also list more than one block, and it will fill it in with a mix, like this:
//set red_wool,red_terracotta  

Note no space between items, just the comma.  

And you can specify percentages, like this:
//set 80%red_wool,20%red_terracotta
//copyStand in a spot relative to your selection and type this to copy your selection. When you paste the selection, it will paste in relative to your new location.
//pastePastes the selection. The spot your standing in when you type paste will be the same relative position as when you copied it.
//undoWill undo whatever you last did. You can also specify how many actions to undo, like this: //undo 3   IMPORTANT: This only works during the session. If you logout and log back in, it will not undo anything you did in a previous session.
//rotate [degrees]After you copy something, you can type this and it will rotate it (in memory), then when you paste it, it will paste in as a rotate version of what you copied.

If you type //rotate 180, it spins it around so that it’s facing in the opposite direction.
//brush [type] [more stuff]Hold a tool, like a shovel or hoe, and type //brush followed by the type of brush and properties. After you do this, the tool will act as that brush.

Example:
//brush tree jungle

When you click your tool on the ground, a jungle tree will appear in that spot.

Two really good brushes:

//brush sphere [block-type] [radius]
If you add -h, the sphere will be hollow.  

//brush cyl [block-type] [radius] [height, optional]
Creates a cylinder or circle. If you leave off the height, it defaults to one block high, so basically just a circle.
Can also add -h here to create a hollow circle.
//mask [block or block list]After creating a brush, you can then type this command to ensure that the brush only changes the blocks you list in your mask command.  

Example:  
//brush sphere dirt 12
Sets your tool to create spheres of dirt with a radius of 12 blocks (pretty big)
Then type: //mask stone,gravel  

Now, when you use your tool, you will replace all stone and gravel with dirt blocks that are within 12 blocks of the place you click. Really handy!