Rulings

• 2021-04-16
  You choose all targets for Magma Opus as you cast the spell. This includes up to four targets for the first effect and two target permanents for the second effect.
• 2021-04-16
  You also choose how the 4 damage will be divided among the first group of targets as you cast Magma Opus. You must have at least 1 damage dealt to each of those targets.
• 2021-04-16
  You must choose two different target permanents for the second effect. You may choose permanents that are already tapped.
• 2021-04-16
  The same permanent can be chosen as a target for each of the two instances of "target." That is, you can have Magma Opus both deal damage to a creature or planeswalker and then tap it. (We're having a hard time imagining why you would, but you're the brilliant student.)
• 2021-04-16
  If somehow all of Magma Opus's targets are illegal as it tries to resolve, none of its effects happen. You will not create an Elemental token or draw two cards.