If this card is Normal or Special Summoned: You can add 1 Level 4 or lower "Magnet Warrior" monster from your Deck to your hand, except "Beta The Electromagnet Warrior". You can only use this effect of "Beta The Electromagnet Warrior" once per turn. During your opponent's turn: You can Tribute this card; Special Summon 1 Level 4 "Magnet Warrior" monster from your Deck (this is a Quick Effect).
If you already have at least 1 Magnet Warrior monster in the graveyard, you can summon Electromagnet Beta and activate its second ability during your opponent's turn. Special summon Delta from your deck and send any Magnet Warrior monster other than Delta. You can send your Delta to the graveyard either by letting it get destroyed, or use cards like Enemy Controller to send it to the graveyard and get Valkyrion the Magna Warrior out to the field.
Dimension Gate banishes your monster, making them untargetable from most cards in the game, useful for protecting your monsters. The second effect will "special summon" them, which will re-activate Electromagnet Beta's first effect again. Even if you don't want to use it on Electromagnet Beta, when your opponent targets your monster during their turn, you can activate his second effect to get Delta from your deck. If Delta is targeted again by your opponent's card, you can then activate Dimension Gate on him. When he's special summoned again, you can send another magnet monster to the graveyard. Simply use cards like Enemy Controller to send him to the graveyard and special summon Valkyrion the Magna Warrior, along with taking control of your opponent's monster.