Scenario
A party that has a Rod of Absorption is facing an evil Sorcerer. The Sorcerer casts a twinned Ray of Sickness at the Fighter and the Wizard. The Wizard is holding the rod.
Would the Ray that is targeting the Wizard be able to be absorbed?
I am unsure whether Twinned Spell Metamagic creates a second spell using the same slot, thus able to be absorbed, or if it is a single spell that now targets two creatures.
Rod of Absorption:
While holding this rod, you can use your reaction to absorb a spell that is targeting only you and not with an area of effect. (DMG, p. 195)
Twinned Spell
When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell. (PHB, p. 102)
Best Answer
Twinned Spell adds a target to a spell, and the spell is still considered to have been cast only once.
The following three questions all discuss the targeting ordeal of Twinned Spell:
But in particular the Twinned Spell Metamagic states:
This shows that you are not casting an additional spell but instead this single casting of ray of sickness is now targeting two creatures. As such a Rod of Absorption will have no effects because it requires the spell to target only the user of the Rod.
Compare the Rod of Absorption to the Arcane Trickster Rogue's Spell Thief feature:
This is something that would work against a Twinned Spell, though it would only change what happens to the Rogue themself, and not the other target as well.