There are many resources in the game: Gems, Gold, Stones, Obsidian, Soul Stones, Soul Shards, Gold Keys, Red Potion, Energy, Portal Stones and Relics.
Gems are the premium currency of the game and can be bought in the shop for real money. Gems can be used to speed up building construction, raise units by trial, buy other resources and energy. You can earn gems from completing missions and arcane portal. The Lord character has a trait to make gem drops more likely in missions.
Gold is used to upgrade units. Gold can be obtained by mining, completing missions, winning sieges, taking part in arcane portal or by buying with gems.
Stones are used to start constructing town buildings. Maximum stone storage is limited by your stone store building capacity. Stones can be obtained by mining, winning sieges or buying with gems.
Obsidian is used to upgrade buildings past lvl 12 and can be mined or obtained via siege.
Soul Stones can be opened in the Hall of Souls to obtain units. There are 3 types of Soul Stone.
Rare - blue - summons 1-3* units
Epic - orange - summons 3-5* units
Mythic - red/white - summons 5* units
Rare and Epic Soul Stones are obtained from missions or arcane portal. A rare Soul Stone can be upgraded to an epic Soul Stone by using Soul Shards in the Hall of Souls. The Lord has a skill that increase the likelihood of a soul stone dropping in a mission. Your Castle level affects the rate of Epic Soul Stones dropping in missions.
Soul Shards are used to upgrade Soul Stones from rare to epic. Click on a Soul Stone in the Hall of Souls and then the 'upgrade' button. Upgraded soul stones have bonus resources when opened such as energy, gold keys, siege stones or red potions. Soul shards can be obtained via opening soul stones, Tree of Life and Arcane Portal.
Gold Keys are used to open gold chests that randomly appear at the end of stage 3 and 6. Gold chests contain gems, gold, siege stones, energy (max 100), gold keys or red potions.
Ressurection (Red) Potion
Red Potions are used to continue a mission when your health falls to 0. The potion gives you 30% health. You can use up to 5 potions per mission. Red Potions are obtained from arcane portal, missions, gold chests and upgraded Soul Stones.
Energy is used to start a map mission. Each mission costs 10 energy. Energy refill stops when your energy is at or over 70, but you have more than 70 energy by obtaining energy from other sources. Energy refills 1 every 2:35 minutes (~23/hr). Energy can be obtained by waiting for refill, or from missions, arcane portal, upgraded Soul Stones, gold chests or buying in the shop.
Portal Stones are used to start a siege against another human player's town guards. It costs 20 portal stones to start a siege. Portal stones can be obtained from missions, Arcane Portal, gold chests, upgraded Soul Stones and from the shop.
Relics are used to upgrade your units. Relics are obtained from missions, sieges, arcane portal and the shop. Some are only found in missions or sieges or arcane portal or daily treasure chest missions. There are 8 different types of relics, 4 for heroes and 4 for guards:
Helm, Weapon (siege), Chest, Ring (arc p/daily q)
Amulet, Totem (siege), Armor, Rune (arc p/daily quest)