Raining Mobs

So basically I made something like the plugin in this video:

Permission:
rainingmobs.use

Commands:

• /rainmobs help - Show help page
• /rainmobs addplayer- Add player
• /rainmobs remove - Remove player
• /rainmobs stop - Stop spawning
  
• /rainmobs players - See active players
  
• /rainmobs player <ticks> <range> <height> <mobs> <time> - Start spawning (players mode)
• /rainmobs world <world> <ticks> <range> <height> <mobs> <time> - Start spawning (world mode)

*ticks: Mobs spawn interval in ticks, 20 ticks = 1 second.
*range: Range in blocks from player
*height: Height from top block at xyz
*mobs: you can add multipile mobs if you split with , "zombie,skeleton"..
*time: optional time in seconds.

How to use: (players mode)
First, add players:
/rainmobs addplayer nktfh100
Then start spawning:
/rainmobs player 20 15 10 zombie,skeleton,creeper,enderman

World mode:
/rainmobs world world1 20 15 10 zombie,skeleton,enderman
It's that simple!

Btw this is my first plugin! :D