Any of the exiled cards you don't play will remain exiled.

Even though the card is named after a specific character, controlling any commander will satisfy its condition.

Once you've announced that you're casting a spell, players can't take any actions until you've finished doing so. Notably, opponents can't try to remove your commander to change how many modes you may choose.

Once you've chosen both modes for the spell, it doesn't matter whether you continue to control a commander. This is true even if you somehow no longer control a commander as you finish casting the spell.

The commander you control doesn't have to be your commander.

There's no extra bonus if you control more than one commander.

Use the number of cards in the target opponent's hand as Jeska's Will resolves to determine how much {R} to add.

You pay all costs and follow all timing rules for cards played with the permission from the last mode of Jeska's Will. For example, if one of the exiled cards is a land card, you may play it only during your main phase while the stack is empty and only if you have an available land play remaining.