BASIC SUMMARY:I thought of this idea after noticing Minecraft does not have a boss that does not require going to the nether or end. This boss is called the CreepScorpion. It is a Spider with a scorpion's tail with a sharp stinger on the end. It also has a creeper attached on it. It fights you by shooting poison with the stinger and by diving at you. When it dies it blows up.

IN-DEPTH INFORMATION OF BOSS:
The boss is as I said a scorpion/spider with a creeper attached on it. Its side is fairly big ( 3 blocks high and 4 blocks long ) and turns smaller every time it loses health which makes it hard to hit him. When it dies the creeper on the Scorpion/Spider explodes with the radius of 3. The mob itself deals 1 heart with poison. Even with such low damage it can hit incredibly fast.

HOW TO SPAWN/ENCOUNTER:
It is impossible to randomly encounter this mob you must follow special steps to create it. You need to drop 3 string,3 bone and 3 gun powder around the same area and lure a creeper. The creeper will take those items and start shining red. Then it will go to the nearest spider and will become a CreepScorp

MINIONS:
The CreepScorpion would spawn one silverfish looking green bug with 6 legs every 5 seconds. Which blow up when near the player. They do 1/4 health but get pretty annoying when lots of them spawn.

LOOT:
It drops A Spider Skull and a random amount of a poison potion or slow potion

WEAKNESSES:
This creature wil turn twice as strong on desert land while it becomes twice as weaker on snow.

OTHER THINGS TO DO WITH IT:
You can right click the CreepScorpion if you slow it,poison it and successfully take 75% of his health . You can control where it goes and where it shoots the poison if your holding a wither star.

BENEFITS TO MC:
This will be awesome if it is added to Minecraft because Minecraft's bosses are extremely hard. It would be good to have a easier boss.