Evolve unlocks at league level 18 and it allows to trade a bunch of cards for a few of higher rarity. No gold is needed for this, but you need to have unlocked the higher rarity card to proceed.

A guild bonus named Self-perfection reduces the number of cards needed to evolve, and some Mini-Event will double the amount of higher-rarities (limited to certain families only).

Exchange ratesEdit

Rare Epic Legendary
Common 50 to 5 500 to 5 /
Rare / 50 to 5 200 to 1
Epic / / 20 to 1

Evolve chartEdit

Here are some charts with all the possible evolutions, updated to Shalloween event (2018-10-26). The sequence the cards are listed is roughly the same in which they appear on SQUAD tab.

Evolve Chart - Chaos

Evolve chart for Chaos units, updated to Shalloween event (26/October/2018)

Evolve Chart - Nature

Evolve chart for Nature units, updated to Forest Hump (10/November/2018)

Evolve Chart - Order

Evolve chart for Order units, updated to Shalloween event (26/October/2018)