Attack leads and garrison cores need different heroes, troop mixes, positioning, and timing.
Basics
Attack leads should scout the current garrison and build from tested current-generation formations rather than copying one universal ratio. Time multiple rallies by actual march duration. Garrison cores switch to defense immediately after capture, report remaining capacity and losses, and verify whose stats the battle report actually uses.
Advanced: same-alliance lead swap
Community hot-swapping changes the defensive core without intentionally emptying the Castle. First confirm that other garrison squads will remain inside. Send the incoming defensive march; when it is only seconds away and no enemy rally is about to land, recall only the outgoing lead's march. After arrival, verify the actual stat provider, capacity, and active skills. Do not use Expel All for a same-alliance lead swap.
Test this behavior in a lower-risk building first because garrison selection details are not fully documented in the official help center.