Drowner of Hope

You can sacrifice any Eldrazi Scion to activate Drowner of Hope's last ability, not just one created by Drowner of Hope.

You can't sacrifice the same permanent to pay two different costs. Notably, if you sacrifice an Eldrazi Scion to activate the last ability of Drowner of Hope, you won't add colorless mana .

Some instants and sorceries that create Eldrazi Scions require targets. If all targets for such a spell have become illegal by the time that spell tries to resolve, the spell won't resolve and none of its effects will happen. You won't get any Eldrazi Scions.