Halvar, God of Battle

The mana value of a modal double-faced card is based on the characteristics of the face that's being considered. On the stack and battlefield, consider whichever face is up. In all other zones, consider only the front face. This is different than how the mana value of a transforming double-faced card is determined.

If Sword of the Realms is attached to a token creature that dies, the Sword's triggered ability will trigger, but the token will cease to exist after going to the graveyard. It won't be returned to its owner's hand.

In the Commander variant, a double-faced card's color identity is determined by the mana costs and mana symbols in the rules text of both faces combined. If either face has a color indicator or basic land type, those are also considered.