When Casal enters, search your library for a Forest card, put it onto the battlefield tapped, then shuffle.
Whenever Casal attacks, you may pay 
. If you do, transform her.
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Vigilance, trample
When this creature transforms into Casal, Pathbreaker Owlbear, other legendary creatures you control get +2/+2 and gain trample until end of turn.
At the beginning of your upkeep, transform Casal.