If i were to use pentarch ward (protection from color of your choice) and i were to combo (enchant) it with Ironfist Crusher (2/4 creature with ability of quot;may block any number of creaturesquot;) would that card be technically quot;impossible to killquot; and i would be able to defend all attacks from then on and be protected from my opponent's mono colored deck? (let's say green) If my question is confusing please let me know and i'll rephrase it.
You pay 3, and play the card from your hand. You examine all of your creatures on the field (only yours) find the card with the highest power. Creatures have X/Y where X is power, and y is toughness, these numbers are written on the bottom right hand corner of the card. (Note: There may be effects in play that are altering those numbers, such as enchanments equipmets, counters etc, you use the altered version of the number where applicable.) So find the one with the highest power, you may have cards that draw for the highest power thats fine, just read out the number. You then have target player lose that amount of life and at the same time you gain that much. If you have a good amount of swamps available to make sure you can play this card, and some strong creatures in your deck, or at the very least some powered up small ones, then sure, it can be useful.
You sort of clarified your question at the end. If you are up against a mono-colored deck and you used Pentarch Ward naming Green, The Crusher could block all attacks without taking damage. It would not be impossible to kill the crusher as the ward doesn't protect itself. Naturalize would first have to work on the enchantment, killing it, then you could destroy the Crusher. Anything that is green and global would affect the crusher (can't think of any such spell at the moment) as it wouldn't target the crusher. But for all essential combat purposes, Crusher won't die.
No, it wouldn't be impossible to kill. When Pentarch Ward comes into play, and you choose to enchant Ironfist Crusher, you must choose a single color for that creature to have protection from. If your opponent is running a mono-colored deck, this creature could be difficult to deal with, but not impossible. First, your opponent can still attack with creatures with evasion, such as flying, shadow, unblockable, and fear. He can also choose to destroy the enchantment, with something like Naturalize. The creature has protection from the color of your choice, but the enchantment can still be targeted, thus causing your creature to lose its protection at an inopportune moment. The Pentarch Ward also doesn't give your creature protection from artifacts or man-lands, such as Mutavault or Stalking Stones, even if their activation cost is the color it has protection from. Lastly, mass destruction spells like Damnation or Wrath of God will still kill the creature, even if it has protection from black or white. It will prevent damage however, so spells like Earthquake or Pyroclasm have no effect on it as long as the Pentach Ward is in place. This is also true for bounce spells. Your opponent cannot Boomerang your creature back to your hand if it has protection from blue, but it can bounce the enchantment back to your hand, causing the creature to lose protection, or by using spells that don't target like Evacuation to return the creature to your hand (in which case, you'll lose the echantment to the graveyard). That's not to say protection from a color isn't good, but it is much better if the creature itself has protection and it is not added through an enchantment.
