The Opera Mate is named after the most famous casual game ever played: Paul Morphy, at the Paris opera in 1858, finishing off two consulting noblemen with a queen sacrifice followed by this exact rook-and-bishop pattern. A rook lands on the back rank right beside the uncastled king, protected from behind by a bishop on the long diagonal.
The shape: enemy king still on its home square, a rook arriving next to it on the open d-file (or e-file), and your bishop guarding that rook from afar so the king can't just take it. It's the classic punishment for a king left in the center too long, which is exactly how Morphy's opponents earned it.
The d-file is open, the bishop on g5 covers d8 from behind, and the black king never castled.
Punish the uncastled king, just like Morphy.