The key ideas when defending against decks with go again is trying to make sure you defend with all the cards you want to, while also insulating yourself from on-hit finishers
However, if your opponent doesnt mind they can use proxy cards in test battles
BPhillipYork: This is a neat way to remove a planeswalker or creature, though a lot of commanders have triggered abilities, those that neat to attack will be mostly knocked out by this, and the ability to long-term remove commander is really powerful
Theres good reasons to send a variety of other options, such as Epsilon the Magnet Warrior if youve got 2+ other names in the yard, or Beta the Electromagnet Warrior to kickstart combos, but all you need to know is that Linear Magnum is the main card youre aiming to open
Phoenix decks will likely be interested in a cheap spell that puts a card into your graveyard and draws a card