This is the official format page for Northern EDH, a.k.a. Mjolnir, a.k.a. Viking Commander.
Northern EDH is a variant on the familiar format with a few tweaks on the existing rules (mostly to bring it in line with what seems intuitive), and a much heavier-handed banhammer.
Northern EDH uses the normal EDH rules (mtgcommander.net) with the following changes:
A player loses the game if they have 20 poison counters.
"Commander damage" (rule 11) is eliminated.
Split cards (but not aftermath) may be included in a deck despite one half of the card being outside of the commander's color identity as long as the other half is completely within that identity. In such a case, only the in-color half of the card may be cast (even if that card has fuse, or is cast without paying its mana cost, or any other such circumstances).

Northern EDH reintroduces Banned As Commander. Welcome back, Leovold.