They don't all have to attack the same one, and they don't have to attack the same player, planeswalker, or battle as the creature with mobilize
During each player's main phase, they may roll the six-sided planar die for a chance to take an action: If it lands on the planeswalker symbol the players must planeswalk and move on to the next plane - put the current plane on the bottom of the planar deck and reveal the next one
This puts the deck in a rough spot, and one thats unlikely to change until a major metagame shift pushes out enchantment removal
Lifegain Cards Let's kick things off with two of the cards that might end up having the most impact on Historic: Serra Ascendant and Soul Warden
If you're playing Commander to have fun, then yeah
Target creature gains trample and gets +X/+0 until end oof turn, where X is its power