Historical Rules · 18 June 2021
Rule 702.71a
Official source text from the 18 June 2021 Rules release
Transfigure is an activated ability. “Transfigure [cost]” means “[Cost], Sacrifice this permanent: Search your library for a creature card with the same mana value as this permanent and put it onto the battlefield. Then shuffle your library. Activate only as a sorcery.”