Blue Storm Dragon, Maelstrom

(This ability is active if you have four or more damage):When this unit attacks a vanguard, if it is the fourth battle of that turn or more, until end of that battle, this unit gets +5000 and ": 1 When this unit's attack hits, you may pay the cost. If you do, draw a card, choose one of your opponent's rear-guards, and retire it.". /:If you have a non-Aqua Force vanguard or rear-guard, this unit gets -2000.