To level up your heroes quickly once they are unlocked, players recommend grinding the "Sunken Citadel"

This report outlines the system in Kingdom Rush Frontiers and addresses the community-discussed methods for accessing all heroes . Kingdom Rush Frontiers is widely considered the best installment in the series due to its creative tower designs and balanced hero mechanics. Premium Hero Overview

To get every hero without individual microtransactions, the best option is the Steam (PC) version . Unlike the mobile version, the Steam version includes all heroes and towers