If you go second, then use this strategy for Junk Warrior. First, use a card like Lightning Vortex to clear the opponent's field. Discard a level 2 card like Speed Warrior to activate it. Next, normal summon Junk Synchron and use his effect to bring back Speed Warrior. Finally, synchro summon Junk Warrior with Junk Warrior and Speed Warrior, and there goes 2300 of your opponent's life points!