Immortality

Updated 16th March: So far below I have the first forty Monster Manual Epic (21+) Tier monsters (up to Gibbering Orb) covered. I'll update more periodically, including epic monsters from other books. I also need to check the errata as I have an early printing of the 4E Monster Manual and I know there were a few damage changes to some monsters.

Revising Epic Monster Damage (4E)

Okay, so why bother revising the damages? Well, in the epic tier, many gaming groups report that monsters are not threatening enough. One of the major issues with this that they don't deal enough damage. Investigation shows that while the math is solid enough, that WotC themselves seem to be straying from their own guidelines (as shown in the Dungeon Masters Guide pgs 184-185). The thread here on ENWorld discusses the matter further.

The following is a list of Monster attacks in 4E, showing which are underpowered with the suggested damage in the Dungeon Masters Guide. Its not strictly errata, but in a roundabout way it is.

The Damage is whats listed in the official source, the Revised Damage is whats suggested for that attack in the Dungeon Masters Guide. The Net Difference tells us at a glance if the revision is greater or weaker. Note that even if weaker in most of the cases the damage would still be higher for the purpose of critical hits. While many suggested revisions are only a few points different in 4th Edition a few points can be quite a lot.

Monster Manual

Monster	Attack	Damage	Errata?	Revised Damage (from DMG)	Net Difference
Astral Stalker	Claw	2d6+8		3d6+8	+3.5
	Throat Dart	1d10+8		2d6+7	+0.5
Atropal	Necrotizing Touch	2d10+10		3d8+10	+2.5
	Atropos Burst	4d8+5		5d10+9	+13.5
Blood Fiend	Claws	2d8+10		3d6+8	-0.5
	Bloodthirsty Bite	1d10+8		3d6+8	+5
Phane	Temporal Touch	2d8+10		3d8+9	+3.5
	Wizening Ray	2d6+9		2d8+9	+2
	Wizening Tempest	2d6+10		3d8+9	+5.5
Tarrasque	Bite	1d12+16		4d8+10	+6
	Fury of the Tarrasque	3d12+16		5d10+9	+1
	Trample	1d12+16		4d8+10	+1
Earthrage Battlebriar	Claw	2d12+11		4d8+10	+4
	Trample	1d12+22		3d8+10	-5
Chuul Juggernaut	Claw	2d8+8		3d6+8	+1.5
	Psychic Lure	2d10+3		2d6+8	+1
Godforged Colossus	Force Weapon	4d12+15		4d8+10	-9
	Defensive Strike	4d12+15		4d8+10	-9
	Force Missile	3d8+11		5d12+9	+17
Death Knight (Dragonborn Paladin)	Soulsword	1d8+16		3d8+9	+2
	Valiant Strike	2d8+16		3d8+9	-2.5
	Terrifying Smite	3d8+16		5d12+9	+12
	Unholy Flames	6d8+14		5d10+9	-4.5
Balor	Lightning Sword	2d10+10		4d6+9	+2
	Flame Whip	3d8+5		4d6+9	+5.5
	Death Burst	7d10		5d12+9	+3
Glabrezu	Pincer Claw	2d8+8		4d6+8	+5
	Abyssal Bolt	3d4+7		2d6+8	+0.5
	Blasphemous Word	1d12+7		2d6+8	+1.5
	Chaos Word	1d12+7		2d6+8	+1.5
Hezrou	Slam	2d10+9		4d6+8	+2
	Bite	2d8+9		4d6+8	+4
Marilith	Scimitar	2d10+9		3d6+8	-1.5
Pit Fiend	Flametouched Mace	2d10+11		3d8+9	+0.5
	Tail Sting	1d6+11		3d8+9	+8
	Irresistible Command	2d10+5		2d8+9	+2
War Devil	Claw	1d6+8		4d6+8	+10.5
	Trident	4d4+8		4d6+8	+4
Blackfire Dracolich	Bite	2d10+9		3d6+8	-1.5
	Blackfire	2d8+8		4d8+8	+9
	Breath Weapon	2d12+8		4d12+8	+13
Runescribed Dracolich	Bite	2d10+10		3d8+10	+2.5
	Blackfire	2d12+8		4d10+9	+10
	Breath Weapon	3d12+8		5d10+9	+9
Ancient Black Dragon	Bite	2d8+8		4d6+9	+6
	Claw	1d10+8		4d6+9	+9.5
	Tail Slash	1d10+12		4d6+9	+5.5
	Breath Weapon	4d8+6		5d10+9	+12.5
	Vitriolic Acid	2d10+6		5d12+9	+22.5
Ancient Blue Dragon	Gore	2d8+10		2d8+10	+/-0
	Claw	2d6+10		2d8+10	+2
	Wingclap	3d10+8		5d10+9	+12
	Breath Weapon	3d12+22		5d10+9	-5
	Thunderclap	2d10+8		2d8+10	-2
	Lightning Burst	5d6+8		2d8+10	-6.5
Ancient Green Dragon	Bite	1d12+10		3d8+9	+6
	Claw	1d10+10		3d8+9	+7
	Tail Sweep	2d12+10		3d8+9	-0.5
	Breath Weapon	3d10+8		5d10+9	+12
Elder Red Dragon	Bite	2d10+9		3d6+8	-1.5
	Claw	2d10+9		3d6+8	-1.5
	Tail Strike	3d10+9		3d6+8	-7
	Immolate Foe	3d10+8		4d12+8	+9.5
	Breath Weapon	3d12+8		4d12+8	+6.5
Ancient Red Dragon	Bite	2d12+12		3d8+10	-1.5
	Claw	2d12+12		3d8+10	-1.5
	Tail Strike	4d10+12		3d8+10	-9.5
	Immolate Foe	4d10+10		5d10+9	+4.5
	Breath Weapon	4d12+12		5d10+9	-1.5
Ancient White Dragon	Bite	2d12+7		4d6+8	+2
	Claw	2d12+7		4d6+8	+2
	Icy Tomb	4d12+9		4d12+8	-1
	Breath Weapon	8d6+9		4d12+8	-3
Dragonborn Champion	Bastard Sword	2d10+9		3d8+9	+3.5
	Furious Blade	2d10+9		5d12+9	+21.5
	Dragon Breath	2d6+6		5d12+9	+28.5
Bluespawn Godslayer	Greatsword	4d6+9		4d6+8	-1
	Bite	1d10+7		4d6+8	+9.5
Efreet Fireblade	Scimitar	2d10+7		3d6+8	+0.5
	Hurl Scimitar	2d10+7		3d6+8	+0.5
	Whirling Firesteel Strike	2d10+7		4d12+8	+16
Efreet Cinderlord	Scimitar	2d10+7		3d6+8	+0.5
	Fire Bolt	2d6+8		2d6+8	+/-0
	Curse of the Efreet	1d6+8		5d10+8	+24
Efreet Flamestrider	Scimitar	2d10+8		3d6+8	-0.5
	Fiery Grasp	1d6+8		2d6+8	+3.5
Efreet Pyresinger	Scimitar	2d10+9		3d8+9	-0.5
	Fire Bolt	3d6+8		2d8+9	-0.5
	Fiery Chains	2d8+7		4d10+9	+15
Efreet Karadjin	Scimitar of Horrendous Flame	2d10+9		3d8+10	+3.5
Ghaele of Winter	Winter's Touch	2d8+9		2d6+7	-4
	Freezing Ray	2d8+9		3d6+8	+0.5
Earthwind Ravager	Slam	2d8+10		3d6+8	-0.5
	Wind Devil	4d8		2d6+8	-2
	Whirlwind	1d8+10		2d6+8	+0.5
	Buffeting Blast	4d8+8		4d12+8	+8
Thunderblast Cyclone	Lightning Arc	2d8+11		2d8+9	-2
	Lightning Bolt	2d8+11		3d8+9	+1.5
	Thunderclap	2d10+9		2d8+9	-2
	Charged Mist	1d10+9		5d10+9	+22
	Lightning Storm	6d8+9		5d10+9	+4
Great Flameskull	Fiery Bite	1d4		2d6+8	+12.5
	Flame Ray	2d8+10		3d6+8	-0.5
	Firestorm	3d6+10		5d10+8	+15
Tormenting Ghost	Spirit Touch	2d8+9		3d6+8	+0.5
	Burst of Terror	1d8+9		4d10+7	+15.5
Death Giant	Greataxe	2d6+9		4d6+8	+6
	Soulfire Burst	2d8+5		3d6+8	+4.5
Death Titan	Greataxe	2d8+10		4d6+9	+4
	Soulfire Burst	2d12+6		3d8+9	+3.5
Fire Titan	Fireraging Greatsword	2d6+9		3d6+8	+2.5
	Hurl Lava	4d6+6		4d10+7	+9
	Burning Wave	2d10		2d6+7	+3
Storm Giant	Crackling Greatsword	1d12+10		3d6+8	+2
	Sweeping Sword	2d8+10		5d10+8	+16.5
	Hurl Thunderbolt	2d6+6		2d6+8	+2
	Howling Winds	1d12+6		4d12+8	+21.5
Storm Titan	Roaring Greatsword	2d6+11		3d8+9	+4.5
	Hurl Thunderbolt	3d6+6		2d8+9	+1.5
	Howling Winds	2d12+6		4d10+9	+12