Advanced format ruling
Union Rider
Card effect (current official text)You can take control of up to 1 Union Monster that is currently a monster on your opponent's side of the field, and equip it to this card. The Union Monster that is equipped to this card cannot be changed back to a monster using its own effect.
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.