Let's say a cockroach is carrying a stack of newly joined neutral creatures into the city to drown them in a pit. An enemy hero (whether it's the main hero or not) sees this, and the question arises: does the presence of the stack of neutral creatures influence the opponent's thinking and gameplay?
1. The main hero attacks the cockroach and wins, but by the time he eliminates all the neutral creatures, the cockroach will have damaged the main hero's own units.
2. A non-main hero might not be able to defeat the cockroach in this situation, so he doesn't attack.

Joining should be prohibited. And without any pits. If a unit accidentally joins, remove it immediately. If the turn time is up, immediately inform the opponent about the fact that a unit has joined. If a battle ensues, do not deploy the neutral creatures into the battle. If it is impossible to separate the neutral creatures, then the entire stack, consisting of both your units and the joined units, is not deployed into the battle.