  Recursed is a 2D puzzle platform video game featuring treasure chests that,
when jumped into, instantiate a room that can later be exited (similar to
function calls), optionally generating a jar that returns back to that room
(similar to continuations). We prove that Recursed is RE-complete and thus
undecidable (not recursive) by a reduction from the Post Correspondence
Problem. Our reduction is "practical": the reduction from PCP results in fully
playable levels that abide by all constraints governing levels (including the
15x20 room size) designed for the main game. Our reduction is also "efficient":
a Turing machine can be simulated by a Recursed level whose size is linear in
the encoding size of the Turing machine and whose solution length is polynomial
in the running time of the Turing machine.
