Harbinger of Titans

When Harbinger of Titans enters the battlefield, search your library for a legendary Eldrazi creature card and put it into your hand.
Whenever you cast a legendary Eldrazi creature spell, return Harbinger of Titans to your hand.
Harbinger of Titans' power and toughness are both equal to the amount of mana you have paid paid to cast legendary Eldrazi creature spells.
Almost as terrifying as its masters. But not quite.