Reveal Garbage Fire as you draft it and note how many cards you've drafted this draft round, including Garbage Fire.
Garbage Fire deals damage to target creature equal to the highest number you noted for cards named Garbage Fire.
8/23/2016 For example, if you draft Garbage Fire as the third card in a draft round and then another one as the twelfth card in a draft round, each Garbage Fire will deal 12 damage. Yikes.
8/23/2016 If you somehow cast, copy, or gain control of Garbage Fire but you didn’t draft one, the highest noted number is considered to be 0, so Garbage Fire won’t deal any damage.