Complex sentence: Readers who write in with mistakes or alternate solutions to puzzles are often rewarded with a GAMES T-shirt; the only other way to obtain a GAMES T-shirt is to be a runner-up in one of their contests.
Split into simpler sentences: Readers who write in with mistakes or alternate solutions to puzzles are often rewarded with a GAMES T-shirt. The only way to otherwise obtain a GAMES T-shirt is to be a runner-up in one of their contests.