Blightbeetle doesn’t remove any +1/+1 counters already on creatures your opponents control.

Creatures your opponents control won’t receive +1/+1 counters as they enter the battlefield.

If a replacement effect allows a player to modify or replace an event by putting +1/+1 counters on a creature affected by Blightbeetle, that player may apply that replacement effect, but they won’t get counters. If the original event is entirely replaced (such as by applying Vigor’s replacement effect), the entire original event simply doesn’t happen.

If the cost of an ability or an additional cost of a spell requires putting +1/+1 counters on a creature affected by Blightbeetle, that cost can’t be paid. If a resolving spell or ability says that a player may put +1/+1 counters on that creature, that player can’t choose to do so.