If I use Viktor's ability to create a token and my opponent reacts with Gust to make me lose control of the battlefield, can I still play the token on that battlefield since I chose the location first?

Ruling: No, you do not choose the location when Viktor's ability is activated. The location is chosen when the token is played after Viktor's ability resolves, so Gust can legally be played in response and you will not control the battlefield when you need to choose where to play the token.

Sequence:

• Viktor's ability is activated and goes on the chain
• Opponent can react with Gust, removing your control of the battlefield
• Viktor's ability resolves and creates a token that goes on the chain
• When playing the token (after Viktor resolves), you choose the location at that time
• Since you no longer control the battlefield, you cannot play the token there

Nuances:

• The location choice is part of playing the token card, not part of activating Viktor's ability
• Gust is a legal play because it doesn't create an illegal state itself - the battlefield being controlled by no one is legal
• Tokens use the chain when being played