Super Monster or Super Creature is the name given to certain enemies that appear at the 60th level and beyond, and have stats well over the general maximum of 20. These appear only through summonings such as the Monster Trap or the monster portal opened by RNG (the one exception here is for the Mimic). They are not distinguished from other monsters by the game, but their presence will become evident based on the amount of time it takes to kill them. After about the 100th level, super monsters are strong enough to kill you in one hit.
Super monster's can be put at bay through the knockback power of heads. Since the decapitation chance increases with level, it should be possible to gather a few heads before fighting a super monster. After using the knockback, you may be able to get in some hits with a ranged weapon or some of the other tactics mentioned below.
Because of these super monsters' high endurances, blessed strikes are good for repeated knockback. They also significantly increase the damage dealt, speeding your defeat of them. Again, ranged weapons are best for blessed stikes since they don't risk melee damage dealt by the super monster.
Hexing super creatures with confusion will make hitting them easier, so you will actually be able to deal damage with regular strikes. Ranged weapons are particularly good for these types of counter-attacks.
Since regular attacks don't inflict much damage without blessed strikes, the Fear enchantment is a better way of dealing damage. The speed of the Horror summoned will match that of its target, and the constant damage can greatly damage the monster.
Casting Holy on enemy creatures will either cast smite or an explosion. In addition, no matter how tough or how high a defense the intended target has, the Rune of Holy has a 50% guarantee of killing it in one shot. The other 50% of the time, the explosion will emanate from the super creature rather than the air.
Note: Gun Leeches are pretty good because their bullets will bleed the monster as well as regular-damage them, and if you must engage in melee combat with a Super Monster the Gun Leech is also a great melee weapon.
Quickenings are unfortunately only good for running away. The first super monster you encounter may be destroyed, but later on their resistances will grow too strong for the lightning caused by quickenings. Some monsters may also be fast enough to escape them altogether.
Although polymorphing works on creatures like the Balrog who have race-specific stats, a polymorphed super monster will retain its general stats like strength, rendering about the same difficulty as before the polymorph.
It is not recommended to fight super monsters in close quarters. It will take you much more time to damage the super monster, while it is capable of killing you in a few blows. If you must resort to close combat, have Runes of Undead and Heal at the ready.
Stunning allows you to get more hits in on the super creature, but simple melee attacks do very little damage, if they even manage to hit. Stunning can still be used to run away, but not as a reliable combat tactic.
Noteworthy Super Monsters
Super Golems usually appear after chaos wall blocks disperse. These are the most common super creatures you will encounter. Super Golems' massive endurance and defense will shield them from nearly all of your attacks, even with maximum enchantment levels and with Red at level 20. Their incredible defenses will make even blessed strikes seem weak against them.
Even non-super Mimics can become a hassle if they manage to steal your form. Super Mimics do the same, and will also keep their high stats, meaning they can be deadly when you're in a strong form. Mimics will not appear through normal summonings, and, like other Mimics, usually appear as pseudo-chests.
Super Mind Flayers are the easiest of the super monsters to defeat. Their XP-stealing ability will act against them, because you will quicken, heal, and deal considerable damage back to them. If you are attacked by a mob of Mind Flayers, you will find yourself quickening multiple times in a row and decimating their horde.