Elves may not build (in) a base with more than two builders. If your base is destroyed or a base with more than two builders needs help, you may go there to aid with spells but you must not build.
This can be exploited by 3 elves in a base with no buildings but 6 workers .
A 3 end game blades troll cannot even destroy a ultraionic wall while being repaired by 3 elves and 6 workers
here is one example . where this happened
viewtopic.php?f=8&t=93081&p=368805#p368805
i suggest the rule be clarified so people don't make it a excuse to exploit as in my above post
Thank you