(Note: This guide assumes you know the basics of combat (augments, fighting in general, etc) and this is made by a rookie so there may be some tinkering.)

Ruza is a great game, but with a pretty complex battle system. First we'll start off with main characters and the classes they should be put as.
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Jeremy - This lil Anime Blue Eyed character should be mainly DPS, by dealing major amounts of damage. Equip em with 2 weapons.

Ada - The Red Haired woman should also be mainly DPS, pairing together should give major amounts of damage output in total.

Moxy - The female version of The Demoman from TF2, this gal should be focusing on debuffing the enemy with their debuffs or using items.

Gin - The furry is the 2nd most important in the group, maximize healing and do nothing to their damage, maximize their defense gem and nothing else.This is the healer of the group, save up mana so that you always have a spare 5 mana lying around for the Area Heal, if you're high leveled. Gin can fully revive the team to nearly or all HP. This can save you many times.
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Items:
You should probably give as high damage weapons as possible to Ada and Jeremy.
For Moxy, give debuffing weapons and a bit of armor.
For Gin, have as much healing gear and armor as you can.

Strategy:
For easier regular fights, no strategy is needed, just use the correct traits and deal damage.

For harder fights, try to use the Focus as much as you can, but avoid using it from later rounds to save up, if your team is dying,
immediately stop using Focus and save up as much mana as you can. Gin is your last resort, and should be protected at all costs.
(Note: do NOT use gadgets unless ABSOLUTELY necessary)

For Boss fights, it's like last strategy but try to debuff the enemy with as much items as you can, however only do this with Moxy and/or Gin. Moxy is recommended if you DO decide to spend your points on debuffing the enemy on Moxy. It's recommended that the debuff deals damage, as for a CERTAIN boss, they like buffing their gems to MAKE YOU ONLY DEAL 1 DAMAGE TO IT. So for boss fights, bleeding, venom, etc is recommended as the debuff BEFORE you use weakening ones.
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Grinding:
For Chapter 1, it's recommended to grind off areas that are easier, for bandages, debuffing items, damage dealing items, etc.
This will make your life easier and help you in Chapter 2. It's best to get to level 10 and start tinkering with it.
However, some items are outclassed at higher levels BUT do not sell em, for example. Jeremy and Ada deal more damage than a throwing knife at higher levels, but save it for Moxy or Gin if you want to deal the finishing blow on one of them, however, healing items that do NOT buff/debuff should be sold off as late-game Gin outclasses them.
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I hope this guide can help those who decide to have balls of steel and go max difficulty like me. However, this is made by a bit of a higher tier rookie. So don't take this guide to heart and if I make any mistakes or should include something, comment.