Experience is used to advance character levels.
Experience is typically gained through the application of skills. Since practically everything in Elona besides just plain walking has a skill associated with it, (and even walking does on the world map) this generally means players will constantly gain experience in the background without really ever having to notice or care about actively seeking out sources for experience. If a player casts spells, for example, reading a spellbook trains literacy just for reading, and memorization for learning Spell Stock even before you cast a spell. (Which gives casting experience, as well as potentially control magic, Magic Capacity, and meditation, when you recover the MP you spent.) Just reading a high-level spell can give hundreds of experience points, while killing a monster may give only a dozen.
In fact, since you gain experience for each act of attacking (and hitting) a monster, rather than killing a monster, you gain more experience (and skill experience for that weapon) for not killing a high defense monster with a weak weapon than you gain for killing a monster in one hit. You typically gain more experience, however, for passive acts like simply carrying a heavy load, not (yet) being detected by every creature on the map (even friendly ones in town), or recovering spent MP rather than the few turns spent in active combat. Even sleep can train skills like faith through dream events, and eating means finding food, which usually trains anatomy or gardening, and if you start cooking the food, you gain experience for that, as well.
Because of the fact that nearly anything and everything players do gains experience, levels are often more measurements of time than intensity of play.
Player Character Levels
Character levels have an impact on basic character stats - HP and MP are nearly directly multiplied by level, meaning doubling your level will often double your HP and MP totals. (These are multipliers of the HP and MP you get from attributes, however, and as your attributes will likely rise as experience rises, you will probably see sub-geometric growth, rather than linear growth with level.)
Character levels are also used in determining the amount of money generated in salaries, random events, as well as quality and "tier" of items gained by players in events that are not tied to a specific dungeon level, such as treasure map treasures, or items gained from wishes.
Character level, however, also is used in determining taxes (but not in Elona+), and can increase cash penalties in negative events like the malicious hand.
Character level also is used in determining what creatures you can capture with Rods of Dominate, which plays a very large role in determining how powerful your pets can be.
Meanwhile, this game does not usually rubber band monster level to the player - most monster levels are determined by the level of the location you are exploring, or the level of the quest you are on. Some encounters, like rogue bosses, and the level of the quests you can take, are based upon fame, which is a wholly independent stat from character level.
This means there is generally little downside to the player gaining new levels, and the added HP and cash rewards, if nothing else, can mean levels will almost always be a net positive to the player character.
Levels play a far more dramatic role in the capabilities of NPCs than in player characters. Like player characters, NPCs have a race and a class that determines their starting skills and attributes, but unlike player characters, as they need to have their skills generated instantly, those base skill and attribute levels are multiplied by a function of their character level, generally meaning that a level 40 creature of a given race and class will have double the skills and attributes of a level 20 creature.
Because creatures that are not your pets you have specifically gene engineered will not gain any new skills, and will only train skills if you stay on the same map as those NPCs for a decent period of time while they perform actions, race and class, multiplied by level, are essentially the only determining factors in NPC skills and attributes.
Pets and any NPC that somehow perform enough actions to gain experience will also level up on their own from gaining enough experience. Actually doing so, however, is generally rare outside of creatures with single-digit levels due to the infrequency of non-combat skill use and difficulty in keeping potentials high.
More often, pets gain levels through gene engineering, especially through engineering a higher-level creature into a lower-level creature, which tends to level the recipient and potentially give them additional skill or attribute gains.
Elona+ also allows players to use the doujou to essentially directly convert cash into levels for their pets over time.
Ways to increase experience
- Virtually any use of skills
- Blessed potions of descent (instantly gain one level)
- (Elona+) Killing monsters
Ways to decrease experience
- Potions of descent (uncursed; cursed potions of descent will do too, but will decrease your stats)
- Weapons with the "It disturbs growth" equipment attribute (periodically drains experience).