Oghma Infinium

Defender, Hexproof
Target creature gets -0/-X, where X is your
devotion to green and black. When the target
creature is tapped, destroy it. If it were to be
destroyed by other means, create a 0/X green
Champion token with Toxic 1. It becomes the
target of this.
"All seekers of knowledge come to me, sooner or later."