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Level 15 - IGOTFON
The answer to this puzzle is:
Words: TIGON, INGOT, GONIF, GONOF, GOON, FINO, TING, INTO, TOGO, FOIN, GOOF, ONTO, NIT, ONO, FIN, NOT, GOT, GIN, TOO, FIG, FOG, OFT, GIT, NOG
Bonus words:
TIGON, INGOT, GONIF, GONOF, GOON, FINO, TING, INTO, TOGO, FOIN, GOOF, ONTO, NIT, ONO, FIN, NOT, GOT, GIN, TOO, FIG, FOG, OFT, GIT, NOG