The pure power check. One long tower, one floor after another, each demanding a little more combat power than the last — climb as high as your build allows, then sweep it daily.
Tower Challenge is a single, very tall ladder of floors. Each floor is one short fight; clear it to unlock the next. The catch is the recommended combat power, which climbs relentlessly — from about on floor 1 to over at the top — so your ceiling here is a direct read-out of your account's raw power. Every 50th floor is a boss. Once you clear a floor you can sweep it for its rewards without replaying.
Rewards pay Super Keys, Stars and upgrade materials, scaling with depth. The recommended power alongside each milestone shows how steep the wall gets: