Pointed Discussion

Let's say my opponent casts Cancel (or a similar spell). I then can Twincast and choose my opponent's Cancel as the new target. What happens?

I think the first action the stack would be:
-Copy of Cancel cancels first Cancel.

But if that happens, then Twincast has no valid target. And thus the first Cancel shouldn't be affected. I'm sure my reasoning is flawed... because by my understanding this situation should cause a disruption of the spacetime continuum and destroy the universe.

I think it works something like this:

I play blaze for 10,000 damage, targeting my opponent

Stack:
-blaze


In response my opponent plays cancel, targeting my blaze

Stack:
-cancel
-blaze

In response I play twincast, targeting his cancel

Stack:
-twincast
-cancel
-blaze

We both pass and then the stack starts to resolve:

Twincast creates a copy of cancel, and choose my opponent's cancel as the target for mine.

Stack:
-cancel (the twincast copy)
-cancel (my opponent's spell)
-blaze

My cancel resolves and counters his cancel

Stack:
-blaze

Blaze resolves and deals 10,000 to my opponent's life total.

Or you could just twincast your own spell in response to cancel. Same result but easier to understand

Me: I play Shivan Meteor on my Stuffy Doll *deals 13 to opponent*
Opponent: OW!!!!
Me: Oh yeah by the way... twin cast
Opponent: MOTHER FU- *dies*

What happens when you Twincast your Twincast?

@pinneapplesam. Twincast your blaze and save everyone the headache of reading your long and anticlamatic comment.

All hail the blue Fork!

This effect is surely more blue than red, and this card in blue can be devastating! You can:
- copy counterspells to counter other (counter)spells
- copy your own spell before it's countered
- copy opponent's removal spells to remove opponent's best creature
- copy opponent's super-devastating burning spell and throw it into his/her face killing him/her before his/her resolves
...
Very versatile!

@s0phocles and beerious - PineappleSam was just answering the question posed to the board by JTKirk. Some newer players may have something like this come up during their play and not know the rulings.