Each M:tG player represents a planeswalker. It's a simple premise that presents a lot of questions when viewed from within the Multiverse itself. Some of you may have already pondered that there needs to be a multiverse planeswwalker type for each of the M:tG formats of play. From strongest to weakeast they are:
-Block (Yes I know Urza or Mirrodin Block could dominate - speaking in a general sense)
-Elder Dragon Highlander
*The most powerful type of planeswalker is when M:tG first, first came about when there were no limits on card count. You could literally have a deck that consisted of 20 Black Lotus, 20 Lighting Bolt, 20 Ancestral Recall. It's because of this craziness that a limit of 4 spells per deck was put into place. Almost no one plays like this anymore and no sanctioned event would ever consider which would correspond with an 'in universe' explanation why the most powerful planeswalkers are rare.
Even if we were to codify the formats into cool sounding planeswalker types we would also have to explain hybrid planeswalkers. How else would you explain (via the Multiverse) the same player playing Legacy every Wednesday night but at a Standard tournament every FNM? That implies that perhaps it's not planeswalker types that are the issue but the spells themselves that place restrictions upon the planeswalkers.
There would also need to be multiverse explantions for banned and restricted cards and perhaps an extra type of planeswalker: WotC staff who design M:tG sets.
Of course you can dismiss this as a fan just 'thinking too much into it' but that's who I am. And to an extent so are you because look where you are reading this. ;)