Possessed Portal

[B.C.]

Oracle Text: If a player would draw a card, that player skips that draw instead.
At the beginning of each end step, each player sacrifices a permanent unless he or she discards a card.

If a player has no permanents, do they still have to discard a card? I assume yes, but the wording is a little ambivalent to me.

[Rico Suave]

No, a player would not have to discard a card.

The key word here is "unless" which is giving each player an option. Compare for instance another card that uses this term:


Rhystic Study
2U
Enchantment

Whenever an opponent casts a spell, you may draw a card unless that player pays 1.

An opponent can choose to let the player draw, even if he is able to pay that 1.

The same is true in this case; a player can let the sacrifice happen (even if he has nothing to sacrifice) without discarding a card.

[Koby]

More specifically, the necessary condition is the discard - the cost. If you have no hand, and cannot discard a card, then the cost fails, and you would need to sacrifice a permanent - the effect. The effect portion of that ability does not depend on whether you have a permanent or not.