A feature that enhances the basic abilities of a 'Collector' symbol, changing its collection range, targets, or value.

Collector Upgrade is a meta-feature that enhances the basic rules or abilities of a 'Collector' symbol that appears in a bonus round to the next level.

The core of this feature is not just to add a new symbol, but to change the behavior of the 'Collector' itself, which plays a key role in the game, thereby boosting the potential of the bonus round to an unpredictable level.