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Level 11 - IITFHGGN
The answer to this puzzle is:
Words: INFIGHT, TING, NIGH, INTI, NTH, NIT, FIN, GIN, FIG, GIT, TIN
Bonus words:
INFIGHT, TING, NIGH, INTI, NTH, NIT, FIN, GIN, FIG, GIT, TIN