You can choose to target zero creatures. If you do, you’ll still create the Horror token.

This scheme’s effect allows you to play an additional land during your main phase. Doing so follows the normal timing rules for playing lands.

If you choose a target creature and it becomes an illegal target by the time this scheme’s triggered ability would resolve, the entire ability doesn’t resolve. You won’t create a Horror token.

The effects of this scheme’s triggered ability in multiples within the same turn are cumulative. It’s also cumulative with other effects that let you play additional lands, such as that of Explore.