If you increase a spark's defense score, it will not die at the end of the turn. This makes buffing creatures with zero defense very useful, as, for example, casting miracle on an ordinary creature will let you deal 3 more damage per turn, but casting it on a spark will let you deal 6 more damage a turn, because the creature can't use its base attack if it dies. Consequently, creatures with 0 defense are a high priority target for the AI. It seems that Parallel Universe does not have a special exception for this rule, so AI will use it poorly. As others said, there are no AI decks that have the both cards in them, but some levels of AI use randomly created decks which be well suited for AI use and the Arena uses player created decks controlled by the AI, and not all players may be aware that the AI uses that combination of cards poorly.
