Sorry Entropy, but as for timing, "Twin-Headed Behemoth" does not activate until that End Phase. Moreover, if something should happen to "Twin-Headed Bohemoth" between the time it is "destroyed and sent to the Graveyard" and the End Phase, it will not have activated its effect, so it will activate during the End Phase of the next time it is "destroyed and sent to the Graveyard". Note:
• If you activate "Monster Reborn" to Special Summon "Twin-Headed Behemoth" in the turn it was destroyed, its effect has not yet been used, and it will activate the next time it is destroyed.
Goyo's effect does activate at the time Monsters are sent from the Field to the Graveyard, as Entropy stated.