Rakarth said:
On a similar topic, I've read some articles bout decks people have constructed and they all tend to go on about a "win condition", I knew decks were based around a specific theme but not around a certain combo or card?
I think I can provide a very clear example of such a combo deck for you. There are many different kinds, but here's a very simple one...
You might be familiar with the "cycling" ability. If not, know that a lot of cards in the Urza's block sets (Urza's Saga, Urza's Legacy, and Urza's Destiny) had the "Cycling 2" ability, which allowed you to pay two mana to discard the card from your hand and draw a new card. Here's one...
Sandbar Mefolk
There were also lands with this ability, like
Blasted Landscape
My brother was losing against his friends, whose decks weren't very good. So I gave him four copies of
Fluctuator and made the rest of his deck out of one Swamp, 24 of those cycling lands, one
Drain Life, one
Songs of the Damned, one
Haunting Misery, and a bunch of creatures with cycling.
While this deck could start playing creatures and attacking, it wasn't very fast or particularly powerful when it did that. But what it could do was cycle cards for until it found a Fluctuator, play the Fluctuator, then cycle everything it drew for free (except for other Fluctuators, the Swamp, or the three black cards without cycling).
So while the opponent would play some creatures and attack, the Fluctuator deck would drop a Fluctuator on turn two, then (if the opponent couldn't stop it), cycle everything so that it had over 20 creatures in the graveyard, play Songs of the Damned for 20+ black mana, and cast a huge Drain Life followed by a Haunting Misery for good measure.
Of course, in this deck, Drain Life and Haunting Misery were the win conditions. Without them, the deck became a slow deck with small creatures.
Most other combo decks are a bit more complicated and a bit less fragile, but that's the general idea. Note, however, that a deck does not need to be a combo deck (like the Fluctuator deck) to have a win condition. It's just that win conditions are much more important in decks where only a few of the cards can actually win the game. As Turgy has already demonstrated, a deck with 20 small, fast creatures basically has 20 ways to kill you (although none of them are very good at doing it by themselves). A deck that limits its opponent's resources and only has two attackers has a more limited win condition: if the opponent does something to permanently stop both of its creatures, it will not be able to win.