If a spell or ability causes the chosen player to draw cards and then discard cards, Nyxathid's power and toughness changes accordingly as that spell or ability is resolving. For example, if the chosen player has five cards in hand and a spell causes that player to draw two cards then discard two cards, Nyxathid will start out as 2/2, then become 1/1, 0/0, and finally 2/2. This is because cards are always drawn one at a time, but multiple cards may be discarded at once. Although Nyxathid momentarily had 0 toughness while that spell was resolving, it isn't put into its owner's graveyard as a state-based action because state-based actions aren't checked until the spell has finished resolving.