In Brown dust you are always on a quest to upgrade and grow your mercenaries. To do this you will need to collect a number of items from the game. You can farm every single item by playing different-different game modes. Here is a list of the items you can get from each mode.

Gold – Campaign Battles, Event Dungeon, Sell mercenaries/runes

runes – Challenge mode: Rune temple

Crystals – Challenge mode: Crystal Cave

Slimes – Missions, Quest, Events, Campaign, Challenge Mode: Slime Forest

Soul Gear – Co-op Raid

Honor Coins – Arena

Diamonds – Quest, Missions, First-time clear reward

Ancient Coins – Arena

Skill Books – Honor shop, quests/missions/events, trading post