If there are no other players on your team (probably because you’re not playing a Two-Headed Giant or similar multiplayer game), you can’t pass the ball. However, if All-Star Kicker was kicked, its last ability will still give creatures you control +1/+1 and haste until end of turn.
You may reveal a card with assist kicker and discuss how to pay for it before you begin to cast the spell. Targets are chosen for that spell before you choose another player to help you pay for it and before that player has committed any mana to doing so.
For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Marika Lord
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
Playtest cards use a modified version of game symbols, such as {T} and {W}. These modified symbols should be treated as the standard symbols during play.
Playtest cards aren’t legal for play in any tournament format other than Mystery Booster Limited formats. On the other hand, we expect they will spice up a wide variety of non-tournament games (as long as everyone’s on the same page about using them!).
Assist kicker is a variant of the kicker ability. An assist kicker cost is a kicker cost.
Only the assist kicker cost (or part of that cost) can be paid by another player. Any other costs must be paid by the spell’s controller.
