Here is the first of the weekly dragons for the month of July, the thunder dragon. First the M20 statblock:

Adult Granite: HD 21d12+105 (241), AC 28, Bite +27 (2d8), or Breath 8d6 stream of rocks DC 25,  phys+DEX to dodge for half, or thorwn rock 2d6+7.

And now for the Basic Fantasy Statblock

Dragon, Granite

Armor Class: 20
Hit Dice: 7**
No. of Attacks: 2 claws/1 bite or breath/1 tail
Damage: 1d6/1d6/2d12 or breath/1d6 or rock 3d6
Movement: 30′ Fly 80′ (15′)
No. Appearing: 1, Wild 1, Lair 1d4
Save As: Fighter: 7 (as Hit Dice)
Morale: 8
Treasure Type: H
XP: 800

Granite dragons have thick, rock-like scales with small black spots on them. The scales also tend to become for red as they age. They prefer to live on top of ancient mountains or near stone quarries. In order to properly digest their food, they swallow heavy stones in a gizzard type of organ. The bite of a granite dragon is severe due to their hardened teeth. When fighting, a granite dragon prefers to be near a source of rocks. When their breath weapon is not available, a granite dragon will attempt to hurl boulders. Granite dragons are capable of great cruelty. They enjoy swallowing humanoids whole and listening to their cries as they are ground into pieces by the stone in their gizzard. Outside of this rare pleasure, granite dragons are motivated by the urge to live, breed and collect valuable items.

Granite dragons are immune to poisonous gases.

Granite Dragon Age Table
Age Category 1 2 3 4 5 6 7
Hit Dice 4 5 6 7 8 9 10
Attack Bonus +4 +5 +6 +7 +8 +8 +9
Breath Weapon Rock projectiles (Line)
Length - 70′ 80′ 90′ 95′ 100′ 100′
Width - 25′ 30′ 30′ 35′ 40′ 45′
Chance/Talking 0% 15% 20% 25% 35% 50% 60%
Spells by Level
Level 1 - 1 2 4 4 4 4
Level 2 - - - - 1 2 3
Level 3 - - - - - 1 2
Claw 1d4 1d4 1d6 1d6 1d6 1d8 1d8
Bite 2d6 3d6 3d8 3d8 3d8 3d8 3d10
Tail 1d4 1d4 1d4 1d6 1d6 1d8 1d8