Sorry if you think this command sucks, but I have made Minecraft a little more like Terraria. Here are some things you can do: Summon the King Slime boss by throwing a Slime Block and Gold Ingot on the ground, make a Death Sickle by throwing a Stick and a Coal, summon Demon Eyes by throwing on the ground a Spider Eye and Glass Block, and even create a Trophy of King Slime by throwing 1 Slimeball and a Gold Nugget. Please don't tell me bad things about it, I just released it and will be adding more and more all the time.
Your map looks a bit empty with just a few buildings? Then you should check out this City Generator! Add this machine to your world by just using one command in only one command block! After that, you'll get a snowball, that you can throw and which will create large cities consisting of 10 slightly random skyscrapers! These houses have a modern look and blend perfectly into most town environments! (This is one of my older commands!)
I always have problems with creating large landscapes by hand. There is nothing more boring! In order to no longer having to do that, I have already made some structural generators. And this is one of them, this time for mountains and hills! Using some simple 'Only One Command Block' - magic you can easily create icebergs, dirt- and sandstone mountains! Besides that you can create some hills and smooth your environment as well! Another 'Fun Fact': Initially, this command was 40000 characters long. I had to shorten it to 32000 characters.
Skeletons switch to an iron sword when they get close to you or run out of ammo, skeletons can pick up arrows, and you can pick up skeleton arrows. Made with CrushedPixel's To One Command MCEdit Filter