actually you don't need the highest level gun to kill the boss. in th mid of game, when you can afford, start to purchase from shop, firstly +20%loot, then +gunpower, +ammo, then back to upgrade guns & other shop items.
I finsh the boss with LV8 Pistrol, LV4 Strike, LV5 Frame (which seems 50% appear in game), LV5 Crossbow, without Magnet & Angelwings.
Enjou very much on the earlier verison!! Buy new one is too hard to play with - bad interface (difficult to see recources at a glance), bad movies, all very BAD! decided not to play after win 1 round!!
Before Lv15, use different combination as u like. Reach Lv15, raise all speed, attk, def and play ealier stage (but with different modes together to get as much XP as possible). Later u can use MAX. eatherquake to kill all in seconds...LOL
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