A lot of people seem to have trouble defeating the boss at the airport, possibly due to a glitch but possibly simply due to the strategy required. The eye flash that normally indicates an incoming punch or kick attack doesn’t appear, so you are left wondering what to do. You have to watch his arms or legs to see what he’s going to do and then counter that way. Also, he’s weak against dark attacks, so use the KKPPP combo once you buy it.
Level up your equipment purchases equally, with a little bit extra focus on the defensive one. Also, the critical hit bonus, stun bonus, and other items can sometimes go to the neglect pile, but those are extremely important to upgrade, too. Select them from your house and then grind around with them to upgrade them.
The best way to grind, whether for extra levels on your equipment, dropping the cool down bar on the junkyard, or simply for more coins, is to go to the last level that you’ve beaten and play it over and over. Any level that you’ve beaten will become an endless level, with no health boosts and no gold enemies, and no bosses, so simply try to get as far as you can.
One of the more confusing upgrades is the glasses, sometimes, but what each upgrade does is it adds to the number of stats you can see on an enemy when you use them. At the top level you’ll be able to see their strengths and weaknesses, all of their stats, and how many coins you get when you defeat them. The most important is typically their strengths and weaknesses. X indicates an attack that they are strong against. Circle is weak. Double circle is extremely weak. Triangle is weak, but only shows up for the punch and kick attacks, not for the elemental attacks.
Grind on the final boss to earn an absurd amount of coins. The way to do this is to use one combo attack (preferably a four-hit combo with no spell attached, if you still have one), and then juggle the boss for the rest of your hits. Each juggle-hit will earn you around 2,000 coins, so keep this up for as long as possible to earn an absolutely absurd amount of coins.
Getting to the final boss is another way to use your building materials. You have to go to the right side of the map, then tap on the green building. You’ll have to build something out of building materials. You will have to repeat this each time you fight the final boss, so if you lose, grind on one of the old endless levels again a couple times until you cool down the junkyard.