Goat format ruling
Behemoth the King of All Animals

Card effect (current official text)This card can be Normal Summoned or Set with 1 Tribute. In that case, the original ATK of this card becomes 2000. When this card is Tribute Summoned, you can return from your Graveyard to the owner's hand a number of Beast-Type monsters equal to the number of Tributed monsters.
Rulings
- It is possible to properly Tribute Summon Behemoth the King of All Animals with just 1 Tribute. For example, you can Tribute Summon it with Trojan Horse, or use Cost Down and then Tribute 1 monster because Behemoth the King of All Animals is only Lv 5. In cases such as this, either 2000 ATK or 2700 ATK is correct, so the controller can select which ATK it will have.
- If Behemoth the King of All Animals is Tribute Summoned with 2000 ATK, and is then Set or removed from play temporarily, its ATK becomes 2700 points when it is again face-up on the field.
- If you Tribute Summon Behemoth the King of All Animals with 1 Tribute, and Skill Drain is activated, its ATK becomes 2700 points. Even if Skill Drain is destroyed, the ATK remains at 2700 points.
- If you Tribute Set Behemoth the King of All Animals with 1 Tribute, its ATK will only be 2000 points when flipped face-up. However, once it is face-up, if it is Set again, the effect is reset and its ATK becomes 2700 points.
- The second effect of Behemoth the King of All Animals is a Trigger Effect that can be chained to. It is a targeting effect that targets a monster(s) in the GY.
- If you have "Behemoth the King of All Animals" with an original ATK of 2000 because you Summoned or Set him with 1 Tribute, and you equip it with "Megamorph", its original ATK will be 4000 when your LP are lower, and 1000 when your LP are higher.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Goat forum — sourced change requests get reviewed.