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 Level 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 “Trojan Horse” is Tributed to Tribute Summon “Behemoth the King of All Animals”, you still only return 1 monster from the Graveyard to your hand, because it’s the same number as the number of monsters you Tributed to perform the Summon.
If “Behemoth the King of All Animals” is Tribute Summoned with 2000 ATK, and is then flipped face-down 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 flipped face-down 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 Graveyard.
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 Life Points are lower, and 1000 when your Life Points are higher.