Quote from Omnifarious GreyCommandeer.
Quote from YareWell, let's walk through it.
So, Darksteel Colossus is 11/11 and is indestructible. Eater of Days deals 9 damage to Darksteel Colossus, so that damage will stick around until the end of the turn. Next, Last Gasp is played on Darksteel Colossus, making Darksteel Colossus 8/8. At this point we have a Darksteel Colossus that is 8/8, indestructible, and with 9 damage on it. This means we have a creature with "lethal damage" on it, which, after looking at the list I made, means we're dealing with destruction. But, Darksteel Colossus is indestructible, so he isn't destroyed and stays on the battlefield.
The fact that what caused Darksteel Colossus to have lethal damage was an effect that reduced toughness is not relevant by itself. Instead, we have to look at what game rule is trying to put the creature in the graveyard. Here, it's lethal damage, but indestructibility prevents that from causing the creature to "die" so Darksteel Colossus sticks around. If, instead, we had used Induce Despair while revealing a creature with a converted mana cost of 11 or more, then Darksteel Colossus would be put in the graveyard because indestructibility can't save a creature from being put in the graveyard due to having 0 toughness.
Quote from FutagozaHow good has Khalni Heart been for you, Zorak? Just by looking at your list, it almost seems like overkill next to eight fetchlands, four KotR, and four Harrow. =/