If the target spell has a variable number of targets, you can’t change how many targets it has.
17-04-2020
wotc
If the target spell has damage divided as it was cast (like Mythos of Vadrok), the division can’t be changed although the targets receiving that damage still can. The same is true of spells that distribute counters.
17-04-2020
wotc
Once you begin casting this spell, players can’t take any other actions until you’re done casting it. Notably, they can’t try to remove the commander you control to make you pay its cost.
17-04-2020
wotc
If you choose new targets for the target spell, the new targets must be legal.
17-04-2020
wotc
It doesn’t matter whose commander you control. Any one will do. If you have two commanders, you just need to control one of them.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.