Grim/Ark

Menace, Haste
Grim/Ark must attack each combat if able
Grim/Ark enters the battlefield with a soul charge counter
Sacrifice an artifact: place a soul charge counter
on Grim/Ark
If Grim/Ark would take damage, prevent that
damage and remove a soul charge counter, then if Grim/Ark has no more soul charge counters, transform Grim/Ark