I often find certain characters tanking on colors and it would be handy to have their levels temporarily lower.
Lower Level 5 – the boost would go into the 1st, 2nd, or 3rd boost slot, and would apply to the character in the matching character slot.
If I have The Hood in the third rank slot, and I put a single “Lower Level 5” boost in the third boost slot, then he’d be at effective level -5 for that battle.
Make them free, always replenishing to 6.