I've played lots and lots of EDH games, and there's a certain feeling I get when I have something in play that's tough to deal with. Maybe it's an Eldrazi, perhaps a Blightsteel Colossus, maybe it's a combination of creatures all protecting each other. (Avacyn/Melira/Sigarda sort of thing) It's a happy feeling when you have something that's resilient out there, especially because I don't usually play counterspells. There's only a couple of cards I need to fear.
I started thinking...what mass removal spells always do what you need them to?
I am not going to talk about counterspells here, you'll learn in your playgroup how many of those you should deal with or expect. Most blue players are happy to let the board be wiped.
I also am going to avoid targeted spells, as hexproof/shroud is becoming more and more common.
There's not really a shortage of cards that say "Destroy all creatures," and there may or may not be a clause about regenerating tacked on. I'm skipping those too, because while that's useful, it's not always effective for some reason or another. (Indestructible effects being the main culprit)
Mega-bounce spells, like Evacuation or Devastation Tide are only effective against tokens, but sometimes that's what you need, especially in blue.
Cards like Obliterate or Worldfire are certainly effective, but it's hard to generate a win after one of those resolves without resorting to tricks like Oblivion Ring (to hide something away) or Jhoira, suspending multiple things.
Just like my list of things that protect your general, I'm open to having things suggested to me that need to be added to the list. I've tried to get them all, but I am fallible!
On to the list!
Bottom of Library (No Defense)
Terminus - The poster child for this list. Counter the spell or flicker your creature until end of turn.
Hallowed Burial - Its older cousin, and costs both less and more. Tuck some generals!
Mass Exile (No Defense)
Final Judgment - This is a card that doesn't get played enough. Only Misthollow Griffin laughs at this effect.
False Prophet - In my Cleric deck, this does an amazing amount of work as a 'stay away' card. I also greatly enjoy making "Don't force me to nuke the world"-style jokes at a table, so feel free to cast this guy with your High Market in play and watch as the creature decks all attack someone else. Hilarity!
Mass Sacrifice (defended by Sigarda, Host of Herons and Tajuru Preserver)
Living Death - This is removal of the creatures in play, as long as you can handle the graveyard portion.
Living End - You can suspend it, or cast it off of cascade, but it has the same effect as Living Death.
All is Dust - Not too good if someone's got the artifact deck, but this takes care of so many problems.
All creatures get -X/-X until end of turn (No defense)
I'm leaving off Infest and the -2/-2 effects like Massacre Wurm, because inn my experience, the token players are good at getting to 3 toughness.
Mutilate - With enough Swamps, this even takes out a Blightsteel Colossus.
Kagemaro, First to Suffer - This needs cards in hand, but being a creature, you might be able to recur his effect.
Bane of the Living - Requires a lot of mana, but since you control the size, you can craft a game where firing this for the right amount saves some of your creatures.
Ichor Explosion - To play this for enough, you need one huge creature...but one creature wasn't going to save you from the crowd of creatures on the board.
Flowstone Slide - Another expensive effect, but since you can manipulate the X involved, it can save some of your bigger creatures. Alternatively, use it and then attack, for an Overrun effect.
Havoc Demon - It's a set size, and they might see it coming. That said, -5/-5 will solve a lot of your problems.
Black Sun's Zenith (defended by Melira, Sylvok Outcast) - It goes back into your deck, and has a permanent effect, even on the things you don't kill. I've seen this cast for 10 against a Darksteel Colossus, which is a far more amusing solution than just killing it.
Mass Changes (creatures are no longer a problem)
It was pointed out to me that instead of killing creatures, you can just make them more reasonable. Added to other 'normal' wrath effects,
Humility - Hoo boy. This card has pages and pages of rulings, plus layer interactions, but yeah, it makes everything just fine. Doesn't slow a storm of Saprolings, though.
Sudden Spoiling - I've played this in response to someone else's wrath effect, to deal with a player whose board is a problem. Works like a charm.
Ixidron - This can cause a lot of problems for some decks, but it doesn't affect tokens at all.
If there's other mass removal solutions that don't depend on damage or destruction, let me know!