View source for Treasures of the Deep

=== Bonus BT points ===
Bonus BT points are awarded based on the single highest-rarity special unit that you deploy. Bonuses do not stack, and your allies' units do not count.

The bonus appears to be:

* 3-star unit: 1.05x multiplier
* 4-star unit: 1.1x multiplier
* 5-star unit: 1.25x multiplier
* 6-star unit: 1.5x multiplier
* 7-star unit: 2x multiplier
* 8-star unit: 2.5x multiplier