A few years ago, giant 6"x9" cards were used as prizes for the Arena league. These cards were usually just large versions of existing cards, and they often had a prize marker or some other special indicator on them.
One such 6"x9" card was given away in a "Serra Angel" comic book that was released in 1996. The enlarged Serra did not have the normal Douglas Shuler artwork, but rather a reinterpretation of Serra by Rebecca Guay. This is one of the most sought-after oversized cards.
Note that another oversized Serra Angel featuring the actual card art was produced and given away as part of Wizards' "Caravan Tours" in 1995 and 1996.