Possessed Nomad

The flavor and the rules agree more pointedly than most threshold designs manage: this is white getting corrupted by the very mechanic its surrounding block prized, with graveyard count as the resource and identity loss as the consequence. Fill your bin to seven and a dutiful 3/3 warden grows, changes color, and learns to destroy white creatures for a tap and three mana (). The Horror in its type line is on the card from the start, but the betrayal it names only arrives once threshold flips the switch. The color swap is the load-bearing piece. Becoming black means white removal that targets "white creature" can no longer touch it, while the activated ability lets it hunt the very color it used to defend. Vigilance, present from the first turn it lands, is the tell that the card wants to hold the line and still swing: a guardian that defects without giving up its post. It belongs to a small line of threshold transformers built across the color pie, each one sliding off-color once the graveyard fills, and this is the white member, the one whose change reads least as a power boost and most as an act of treason. A 3/3 with vigilance for four mana is plain on its face; the whole pitch is what it stops being, and what it turns against, once you have buried half your library.