/usr/games/xletters-duel is in xletters 1.1.1-5+b1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 | #!/bin/sh
nc.traditional -l -p 9090 | xletters -duel | (sleep 5; nc.traditional $1 9090)
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