Advanced format ruling
Mystical Sheep #1
Card effect (current official text)You can substitute this card for any 1 Fusion-Material Monster. When you do this, the other Fusion-Material Monster(s) must be the correct one(s).
Current rulings for this card are maintained by Konami.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Advanced forum — sourced change requests get reviewed.