Eldritchess

You're sitting across another person in a dark forest. Before you lies a board filled with horrifying pieces. Whether you know it or not, you will soon settle a dispute between two ancient beings way beyond your comprehension.

Each player has 9 pieces, mostly based on traditional chess pieces. When a piece is defeated, it goes to the other dimension, which can hold up to three pieces. These pieces can be freed by placing a piece on the other player's key.

In order to win, each player has to either defeat every single one of their opponent's pieces, or place all of their pieces on the place where their opponent's pieces first appeared.