Stack Ethernals, stack $C.
Here’s how the bonuses work:

♟️ Collector Boost – Hold 2 / 4 / 8 / 16 to unlock more $C bonuses
♟️ Rarity Boost – Rare and Legendary Ethernals come with added $C rewards

Legendary = Trait Background → Void (24 pcs)
Rare = Trait Background → Special Effect (105 pcs)
Common = anything else