The annoying long skill animations play all of the time unless you enable to option to disable it during auto battle runs. Low summon rates, poor currency balance, bosses get stronger over time, the game needs a balance overhaul. Game pretty much expects you to buy packs unless you get very lucky as f2p. This is coming from someone who played a similar game for 6 years. The stage drops as you get to higher stages waste more energy and drop way less often.