Once per turn, during the End Phase, if this card was banished by its effect this turn: Special Summon this banished card
However, this will be time consuming and a project for another day
2: This card gains ATK equal to the result x 500 until the end of this turn
Not only can you Special Summon it straight from your Hand while you have no other monsters on the field, it also serves an incredible purpose of being able to summon other Resonator monsters from your Hand or Deck
There are some concessions made to having flexible sideboard cards so that you can be prepared for a wide variety of matchups, but those concessions are only made to the minimum amount necessary to have cohesive sideboard plans and not a single card more because the ideal is to have the highest potential cards possible in games 2 and 3
Lets say I have 2 monsters on the board, and for this example lets just make them both have 1500 ATK (this amount is arbitrary)