Imbalance

Some may find the information on this page subjective or irrelevant.

Imbalance is a feature of game when something (hero, creature, faction, spell, etc.) delivers strong advantage (overpowered) against analogues of its tier, or strong disadvantage. In tournaments players of same skill are expected to have equal chances of victory regardless of random effects, so this presents a problem.

Please note that imbalanced units doesn't always mean strong units. For example, Vampire Lords are weaker than Unicorns and War Unicorns, being two levels down. However, the latter are not the strongest 6th level unit. Their blinding ability is not unique (as some other units have petrification which works in a similar way), the chance they will use their abilities is not 100%, and neither blinding nor aura of magic resistance are a complete disaster for the enemy. As opposed to them, life drain works always unless there is a unit immune to it (e. g. other undead creatures), and it can increase dramatically the chance of winning a battle, lowering the casualities. Unicorns are strong, rather fast, and very mighty in a battle, but there are some other units which can be used in a similar way, while there is no one like Vampire Lords.

Some units aren't very powerful but have great abilities. For example, Harpy Hags and Wolf Raiders are not strong themselves, as they are only 2nd level units and thus have low stats, but their abilities (respectively, to attack without retaliation and to come back, and to strike twice) make them a formidable force and are extremely helpful to the entire army.

Most units become really overpowered only after being upgraded, and their upgraded dwellings often require magical resources (e.g. Crusaders, Titans) or even specific buildings (e.g. Black Dragons, Mighty Gorgons). Imbalanced units are usually very expensive themselves. On the other hand, many shooting and flying units (e.g. Grand Elves and Master Genies) are fragile and not very strong.

Finally, some imbalanced abilities are in fact a double-edged sword. These controversies include, most notably, magic immunity of Gold Dragons, Black Dragons, and Magic Elementals, which makes them immune to damage spells (therefore allowing you to use Dragogeddon strategy), but also to benevolent spells, including Resurrection. Anti-magic spell can save a stack from something very bad, but also makes it immune to supporting spells. Many players criticize Magogs and Liches for their ability to damage their own troops, while they were meant to be able to attack multiple enemy stacks simultaneously; same for breath attack which may cause horrific losses of allied units.

Entities

Factions

Conflux is considered imbalanced because of the combat statistics of its 1st (Sprite), 2nd (Storm Elemental) and 6th level (Magic Elemental) units; and also the quick growth and the Fire immunity of its 7th level unit (Firebird and Phoenix); as well as its Grail Building, Aurora Borealis, which fills the Mage Guild of that town with all unbanned spells.
Necropolis is considered imbalanced because of ability to create huge armies of skeletons, as well as having the Vampire Lords.

Units

Imbalance abilities

These are abilities of 1-6 level units which can make a hero undefeatable. Important: many of these abilities are used only by upgraded creatures, whose basic versions aren't very useful (e.g Pit Fiends and basic Vampires are unlikely to be brought to a battle until upgraded).

Double attack (Crusader, Wolf Raider) and double shoot (Marksman, Grand Elf)
Jousting (Cavalier and Champion)
Binding (Dendroid Guard and Dendroid Soldier)
Spell casting (primarily Master Genie; however that should be used carefully, as Master Genies' spells are random)
Demon farming (Pit Lord)
Life drain (Vampire Lord)
Death blow (Dread Knight)
Strike and return without retaliation (Harpy Hag)
Lightning strike (Thunderbird)
Dispel and Weakness; speed 13 at 3rd level (Dragon Fly)
Death stare (Mighty Gorgon)

Secondary Skills

Spells

Heroes

Artifacts

Buildings

Tactics

Dragogeddon

Methods against imbalance

Banning offending entities from game altogether
Gentleman's accords so even if its in game, it will be not used (e.g. it might be forbidden to upgrade Vampires to Vampire Lords)
Designing map in a way so even if entity is ingame its effect would be countered (e.g. artifacts against necromants, or multiple mid-tier creature dwellings which are not useful for necromants)
And, last but not least, countering imbalance by your own play, tactics, and strategy.