OMEN to POOP.

Every letter change

1. OMEN → OPEN: change letter 2 from M to P.
2. OPEN → OPES: change letter 4 from N to S.
3. OPES → OPTS: change letter 3 from E to T.
4. OPTS → OATS: change letter 2 from P to A.
5. OATS → BATS: change letter 1 from O to B.
6. BATS → BOTS: change letter 2 from A to O.
7. BOTS → BOOS: change letter 3 from T to O.
8. BOOS → BOOP: change letter 4 from S to P.
9. BOOP → POOP: change letter 1 from B to P.