All plants, including "Premium" ones from the original game, are unlocked through gameplay or bought with in-game currency. New Worlds: Features custom worlds like Holiday Mashup Steam Ages Caliganous Carnival No Plant Leveling:
"Here goes nothing!"
Yes, but the upgrade costs have been slashed. You can unlock your 8th seed slot for in-game coins, not real cash.
“Plants! We need defense!” Dave yelled.