Goat format ruling
Goblin King

Card effect (current official text)While you control another Fiend-Type monster, this card cannot be attacked. The ATK and DEF of this card are each equal to the number of Fiend-Type monsters on the field (excluding this card) x 1000.
Rulings
- If you have 2 Goblin Kings, or a Goblin King equipped with Raregold Armor and another Fiend monster, your opponent cannot attack.
- Goblin King's second effect includes Fiend monsters on your opponent's side of the field.
- Face-down Fiend monsters are not included for Goblin King's second effect.
- If you equip Megamorph to Goblin King, Goblin King's ATK is 0.
- If you have a Fiend monster and a face-down Goblin King, and Goblin King is attacked, Goblin King's ATK/DEF increase after he's flipped face-up, but before damage calculation is applied.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Goat forum — sourced change requests get reviewed.