There's a subset of cards with effects that let you attack with defenders, usually templated as X can attack as though it didn't have defender. It's a common line used on defensive filler creatures in Limited, like Platypus-Bear, but let's look at the effects that give this freedom to your defenders more universally: Animate Wall Arcades, the Strategist Assault Formation Felothar the Steadfast High Alert Rolling Stones The Pride of Hull Clade Wakestone Gargoyle Walking Bulwark Warmonger's Chariot Also note that removing abilities from a creature gets rid of defender, so an effect like Dress Down or a bestowed Trickster's Elk would allow a defender to attack
Its too slow for anything but Commander, but its excellent there as a source of many continuous effects: cast from exile, card draw, life loss, and so on
Cards with enter the battlefield (ETB) abilities are easy to find
If you decide to sell your cards online, make sure to factor in shipping costs and fees
The catch here is that you can just float a ton of mana, resolve Upheaval, then use what mana you have left to deploy mana rocks and threats
Exile the rest