The bar is your clock
Gems drop from every enemy you kill. The more you clear, the faster the bar fills. Level-ups arrive in a steady rhythm once the screen gets busy.
Each level opens the same small menu. You choose one card. The run pauses while you decide, so there is no pressure to rush.
What the cards mean
A new weapon card adds a weapon you do not own yet. A weapon upgrade raises a weapon you already have. A passive card adds or improves a support item.
New weapons broaden what you can hit. Upgrades deepen what already works. Early on, one or two upgrades beat a shelf of new toys.
Read the gaps, not the rarity
The best pick is the one your build lacks. Missing area coverage? Take it. Already drowning in single-target? Skip that card.
The gold and shops page covers the other economy that runs alongside gems.