Battlebond: mechanics

Battlebond is the first-ever Two-Headed Giant-focused Magic booster set. It will be released on June 8. Let's lean on its mechanics

• Assist lets another player pay the generic mana cost of your spell, this way helping you to cast it. You don't choose the player until after you've revealed the card with assist and made all other required choices, including targets.
• Partner with [other card]. "When this creature enters the battlefield, target player may put [other card] into their hand from their library, then shuffle." Note that not all the partners in Battlebond are legendary. There are eleven of these pairs. Each pair of partners can co-serve as a deck's commander. This is largely the same ability as the original partner, which debuted in Commander (2016 Edition)
• Support is a returning mechanic from Oath of the Gatewatch.