Wyrms (said: worms) are over world dragons, and have two forms, Normal, and Greater.
Found in level 20+ area, the Wyrm if a large (10 long, three high, five wide) mob, and it is reminiscent of the Red Dragon of D&D. It will blow a fireball, and this will make a TNT sized explosion. The Fire ball will lit any flamable blocks within a sixteen block radius. It drops 5-10 gold ingots, and 0-1 dragon scales, and with which dragon scale armor can be made. They fly around, looking for players to feast upon. They have 750 HP.
The Greater Wyrms live in caves, and are 1.5 bigger. You may be reminded of Smuag. In any cave big enough to house one, in a level 25+ area, will have a one in ten chance of having a large chamber with a Great Wyrm in it. Their Fireball does three TNT's worth of damage. Their fireball lits any coal ore blocks in a sixteen block radius, unless they are covered by something, and if it hits stone, a single block of lava if formed. They can also hit with their tail, doing 5 points of damage, and knocking you back three spaces.
They drop 1-9 Diamonds, A full health Diamond edge, and 1-12 dragon scales. It has 1500 HP.