All games in the Earth Defense Force series have multiple Difficulty Levels which determine a variety of factors including the strength and durability of enemies and the quality of weapon drops.
There are five difficulty levels, Easy, Normal, Hard, Chaos, and Inferno.
There are six difficulty levels, Easy, Normal, Hard, Extremely Hard, Inferno, and Impossible. Unlike all other games, Impossible is not available immediately: unlocking it requires all missions to be cleared on all other difficulties.
Similar to Monster Attack, there are five difficulty levels to choose from: Easy, Normal, Hard, Hardest, and Inferno.
There are three difficulty levels, Normal, Hard, and Inferno, making it have the least amount of difficulty levels of all games. The difficulty level affects experience gains, the durability of vehicles, and the level of weapon drops, as well as the maximum level the player's chosen armor can achieve by gaining experience.
The selected difficulty also determines a Ticker's explosion time.
2025 has the same five difficulty settings as 2017: Easy, Normal, Hard, Hardest and Inferno. As the difficulty level increases, enemy speed, attack rate, durability and damage is increased; many enemies will also fire more projectiles per shot at increased difficulties. This also applies to friendly NPCs, who will deal more damage and have more health at higher difficulties.
Drops are scaled by difficulty level, as is the range of available drops: the ranges are 4, 4, 12, 55 and 60 levels, meaning that getting a specific drop is less likely at higher settings. The difficulty setting also affects the weapon level cap and HP cap in online mode.
In co-op and online, the difficulty level also affects how friendly fire damage is handled: respectively, it deals 10%, 20%, 50%, 70% and 100% of normal damage. On Inferno difficulty, friendly fire damage from explosive weapons will also knock down other player characters; on all other difficulties, it will not. Regardless of difficulty, NPCs do not deal friendly fire damage.
4.1 has the same difficulty settings and mechanics as 2025, with some additions: on levels after Crimson, the levels themselves are sometimes changed at higher difficulties, with extra enemies or tough Mutants added to the standard spawns.
Unlike 2025, vehicles pre-spawned in missions also increase in damage and durability as the difficulty is increased: rather than the BMX10 Proteus in the online-only mission Mountain Giants always being level 28 (making it useless at higher difficulties) it has stats based on the difficulty, exceeding any deployable variant on Inferno.