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.
It can fill your hand with monsters from graveyard and make it reusable.
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.
Low defense of 1500.
With low ATK for 1 tribute summon monster.
Tips, related cards, skills
Trojan Horse and Cost Down
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 "The 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.
Since it can be summoned with 1 tribute, soul exchange can be a great card to support it.