Training is the process of increasing the level of one of your creatures. All of your creatures can undergo training except for Goblins. Training a creature costs a creature-specific amount of resources and time per level; the amount of each resource required will increase and/or the type of resources required will change every 10 levels. The training time will also increase as creatures gain levels, but this increase can be less noticeable between tiers depending on the creature. The resources required to train a creature for each "tier" of 10 levels can be found in the page for that creature or on the Creature Training Summary page. Training increases both a creature's combat statistics and its upkeep per hour by 20%, and at higher levels this often requires players to balance the two for optimal performance.
Creatures at lower levels will require a Proving Ground to train, and will only be able to train to level 10 until creature-specific furniture has been crafted and placed in the appropriate room to increase their level cap. The bonuses of such furniture stacks with other level increasing furniture for that creature. The max level attainable by a creature has yet to be determined, as Settlement Reprisals have contained creatures at or over level 200. The Arena or the Spellcasting Chamber is required to level any creature beyond Level 100. Some upper-echelon creatures can only be trained in either the Arena or Spellcasting Chamber.
Many creatures have something they specialize in, such as a tank or a ranged attacker or a melee DPS. In order to ensure that creatures retain their assumed roles, some creature statistics will not increase through training. These include: attack, defense, speed, healing rate, range, overland speed, resistances, the tank parameters, and pillage if the creature starts with 0 pillage. In addition, the statistics that do increase will change at creature-dependent rates - clearly an ogre will gain more health per level than a warlock, but the warlock will gain more damage per level than most other creatures.
A creature will continue training if it is sent to raid or pillage.