Ancient Dragon, Tyrannoquake

:[Legion 20000]"Ancient Dragon, Tyrannobite"(If your opponent's vanguard is grade 3 or greater, this unit may return four cards from your drop zone into your deck once, search your deck for the specified card, and Legion) :During your battle phase, when your rear-guard with the same card name as a unit on your is put into the drop zone, if this unit is [Legion], this unit gets +5000/ +1 until end of turn. This ability cannot be used for the rest of that turn. :[Choose one of your rear-guards, and retire it] When this unit attacks a vanguard, you may pay the cost. If you do, this unit gets +5000 until end of that battle.