I wonder if by tabletop rules Sorcerer can use Metamagic to any spell they are casting, or if they need to use their own.
For example ... if i cast Ray of Sickness using Staff of Crones ... can i improve it by Twinned Spell?
In fact, Sorcerer is unusual compared to other classes, in that the spells actually do NOT need to be on your own class list for you to apply your class features to them. Sorcerers can apply their metamagic to ANY spell they cast, regardless of where they get it from, as long as the metamagic is appropriate.
Casting a spell from an item is still you casting a spell, and all that that entails - it can be counterspelled, because the enemy is 'seeing you cast a spell', if you use the ridiculous rule about it, it will count as you casting a spell for the casting limitations (that is, you couldn't cast healing word as a bonus then use an item to cast anther levelled spell as your action), and in this point, it's you casting a spell and so you can apply your metamagic.
Sorcerers are unusual in this respect, however:
Most classes require a spell to be counted as one of their class spells in order to be used with most of their other class features. The common phasing you might see in many other places skimming through the handbook is "When you cast a [class] spell you know". It's also why when you get expanded spell lists or extra spell picks they use the specific language "and it becomes a [class] spell for you" in many places - so that it can work with your features.
Edit: So, yes, you *Should* be able to twin cast ray of sickness when casting it from the staff. Should. We'll have to wait and see whether Larian thought of this; as their game engine currently stands, I wouldn't expect that to work off base, and they'll need to make special extra work for themselves to accommodate it.
Edit2: My brain reminds me that it may be tangentially relevant to mention that, for Wild Magic Sorcerer in particular, their Wild Magic Surges are, specifically, only related to your Sorcerer Spells - using the above mentioned language styles.
So, for example, a wild magic sorcerer that took Magic Initiate (Bard), and picked Dissonant Whispers as one of the spells for it, COULD twin spell dissonant whispers, using their metamagic, but they COULD NOT trigger a wild magic surge when casting it, because it is not a sorcerer spell and has not been made one for them.
