Sylas of Dregbourne

Once in the battlefield, no player controls
Sylas of Dregbourne.
Whenever an intant or sorcery is cast, or a card
ability is used, put a Petricite counter on this
card. Sylas of Dregbourne is Hexproof while it
has Petricite counters.
At the beginning of your upkeep, if Sylas of Dregbourne has 5 or more Petricite counters: Transform Sylas of Dregbourne