Some friends were wondering about the interaction of
Brisela, Voice of Nightmares and fuse spells (say,
Flesh // Blood.)
The process of casting fused FleshBlood is as follows:
702.101a (…) If a player casts a split card with fuse from his or her hand, the player may choose to cast both halves of that split card. This choice is made before putting the split card with fuse onto the stack. (…)
601.2a To propose the casting of a spell, a player first moves that card (or that copy of a card) from
where it is to the stack. (…)
(announce modes/targets/etcetera)
601.2e The game checks to see if the proposed spell can legally be cast. (…)
(pay costs etcetera)
This suggests that Brisela does not interfere with the casting. By the time legality is checked, we're talking about a fused FleshBlood with a CMC of 7.
However, there's also this:
708.2b If a player casts a split card with fuse from his or her hand, in addition to choosing either
half as described above, the player may choose to cast both halves, resulting in a fused split
spell. Both halves are evaluated to see if the spell can be cast. If either half can’t be cast, then
both halves can’t be cast as a single spell.That
could be interpreted to just refer to things like “you must have legal targets for both sides”. Does it also mean that Brisela stops this?