wat r combos?

like alaraph achernar.

combo is a new keyword ability that was released in the last set. to play a combo ability, you need to immediatly have a specified card in your card pool to play the combo enhance. so for the combo card you mentioned

the previous card in your card pool must be a low attack card (so something like say dark force: mirage body off of all) then you played the above card, you can play the combo ability to draw 2 cards, however, if your opponent caused other cards to end up in your card pool (say a face down card caused by know when to talk) you no longer have the combo set up, unless you are somehow able to remove the offending card (or play another low attack, then play alaraph achernar.)

Just in case kiit's explanation didn't do it for you:

From the Advanced Game Rules:

"2.9.0.6 Played abilities that are preceded by the term Combo (i.e. Combo E:) can only be played if the requirements indicated in the parentheses following the Combo keyword are fulfilled. (See 2.14.2.2 Combo Keyword)."

So there's a Combo Keyword up at the top (which includes stuff in the parentheses). The stuff in the parentheses are prerequisites for playing the Combo E ability that appears later on the card. If you don't have the prerequisites in the cardpool before this card (in the specified order), then you can't play the Combo E ability at all.

So Combo cards are more powerful (have more abilities available) if you have certain other kinds of cards before them in the card pool.