Well, if they are weak on wisdom saves, hypnotic pattern and a host of other will saves might have clued them in long before.
By the time a party is hitying 6th level tier 3 spells, some counter and recovery potential should be available.
But as GM if you are determined to put it in and also worried it can cause too great an impact, one option is to provide expendable counters along the way.
Maybe over time the minions have collected countermeasures to help them keep their wits. Maybe it happens as other who knew it was a threat came in prepared but got killed and looted by minions.
Even a couple potions of charm immunity can swing the results.
Another consideration is how the damage clause comes into play as far as initiative plays out.
If the battle is group on group, with suggester in the middle, there is no obvious sign afaik that suggestion has worked. So some of the minions may go before the pc gets to act on the suggestion. Their attack might break some free.
Goid help is hard to find, esp if beasts are involved.
By the time a party is hitying 6th level tier 3 spells, some counter and recovery potential should be available.
But as GM if you are determined to put it in and also worried it can cause too great an impact, one option is to provide expendable counters along the way.
Maybe over time the minions have collected countermeasures to help them keep their wits. Maybe it happens as other who knew it was a threat came in prepared but got killed and looted by minions.
Even a couple potions of charm immunity can swing the results.
Another consideration is how the damage clause comes into play as far as initiative plays out.
If the battle is group on group, with suggester in the middle, there is no obvious sign afaik that suggestion has worked. So some of the minions may go before the pc gets to act on the suggestion. Their attack might break some free.
Goid help is hard to find, esp if beasts are involved.