Archetypes of overpowered characters

If any of your classes in the endgame resemble this, the game mechanics are broken. Balance requires to avoid creating these "desirable" archetypes(player would want to play them and demand them to exist) from ever occurring and ruining the game for every other character build(i.e. casuals and normal players).
Archetypes of overpowered characters are desired by players, but allowing them is a design mistake which breaks balance.

1.The Immortal:
Immortals are Tanking taken to the extreme, massive health and regen combined with damage reduction modifiers result in this character losing life much slower than gaining it back.
a.A subtype: Fast regen - oriented at regaining life very fast and having maximum life possible. Regen is often aided by damage-absorb and on-being-hit bonuses/perks/effects.
b.B subtype: Damage reduction - stacks damage reduction items/skills/resistance to achieve near zero life loss, with massive life stats and decent regen rate.
c.C subtype: Damage reflection & regen - reflects near 100% damage and has enough regen to compensate loss of hit-points.
Some variations use on-being-hit modifiers to refill health and reduce damage.
d.D subtype: damage redirected to some other stat, like life->mana with fast mana regen.
e.E subtype: redirects 100% of damage to external pet/summon/entity which is healed/revived by aura/regen items automatically.
Typically such characters ruin both PvP(cannot be killed) and PvE(infinite tanking of monsters) balance, with corresponding band-aid solution is use of percentage-of-life reducing skills/effects or unblockable damage.

2.The Evader: This character has 100% chance to evade/dodge attack or 0% chance to be hit.
a.A subtype: Has 100% blocking of all attacks.
a.B subtype: has 0% chance-to-be-hit due stacking items/skills giving modifiers to it.
Evader is the cousin of Immortal with less of staying power.
Typically such characters are defeated by area of effect spells/skills or non-dodgeable projectiles, for which Evader either prepares or flees. A typical solution is hard cap on evasion chance (e.g. 90% chance to evade) which forces Evaders to invest in alternatives(borrowing parts of Immortal builds)

3.One-hit Killer:Invests in one key skill/attack to maximize damage output allowing insane values which cause one-hit kills for everything. Such characters easily dominate PvP and single-target combat.
a.A subtype:stacks Damage-Over-Time damage so the target dies after one hit, but can respond at the time.
b.B subtype:stacks on-hit effects(or chance to do X when attacking) which maximize damage: such as buff/debuff that make each hit deadly due stacked effect damage.
c.C subtype: stacks reduce-enemy-resistance/dmg-reduction/defense items to multiply already potent damage output into one-hit kill range.
d.D subtype:"The Assassin": uses in game stealth mechanics to avoid being detected most of the time, allow one-hit attacks and disappearance without much delay. The overpowered aspect is that characters/monsters can't respond fast enough before assassin slips back into "invisibility mode" or often just die.

4.The Flash/Speedster: stacks +speed items and aura/area-of-effect damage to run circles around normal characters and wear them down.Can't be reliably hit as he often wears gear with #2 characteristic(+evade, less chance to be hit,etc) and leaves area as soon as hit. While it seems harmless at first sight in skilled hands the Flash is unstoppable, especially with ranged attacks, AoE spells or following pets/summons/auras.
Often the first to mine resources, collect flags, open chests and any activity that requires close movement is dominated by this type.
Speedsters aren't harmful due speed itself, its the multiplicative power of speed with damage/effects of presence of speedster.

5.The Petmaster: Abuses summons,decoys and pets, to create an invincible AI-driven murder army. The key enabling mechanics are allowing pets/summons/constructs to wear or be affected by items of wearer, stacking effects of auras/items that affect multiple pets, lack of limits on summonables.
a.A subtype:Use quantity over quality, mass armies of revived monsters/summons/decoys which surround and dominate the landscape.
b.B subtype:use specific pet/monster type with overpowered skills/stats/buffs/item-bonuses and revives it/them continuously.
c.C subtype:"The Minefield Generator": uses lack of limits on traps/constructs to create areas filled with traps/mines/bombs and restrict ingame movement - gradually enclosing characters with mines/traps. Only vulnerable when outside his minefields.

6.The Sniper: Maximizes range and uses target-seeking attacks to kill everything before being seen.
In PvP this results in attacks which cannot be replied to due range. Outranges all monsters in PvE and deals enormous damage before monster even see him.
a.A subtype: use One-hit Killer tactics with slightly less range or slower rate of fire, by stacking effect/damage modifiers. Basically a ranged version of One-Hit Killer.
b.B subtype: the machine-gunner, stacks +attack-speed mods with lower damage but high range to clear areas safely.

7.The Aura Abuser: Maximize the offensive capabilities of auras or fields of effects, allowing to clear areas very fast.
a.A subtype: adds +movespeed items to deal damage with area-of-effect hit-and-run attack.(often combined with Speedster)
b.B subtype: overpowered crippling aura which denies enemies movement/attack or debuff which making attacking the aura owner impossible.The aura abuser would then use pets or some low-damage skills to kill enemy trapped in the aura range.
c.C subtype: abuses defensive aura mechanics to remain alive or protected from any harm, as the #1(the Immortal) with use of standard offensive skills to clear areas.