Board Thread:Questions and Answers/@comment-78.174.12.241-20131208212030/@comment-15636815-20150623064855

A complete set always uses the full power of the locomotive. Adler has power 4. Therefore, if you're attaching only 2 wagons, you're leaving off the rest of the set.

You DO NOT need to spend gems. You DO need to use the full power of the locomotive.