Purple nymph is also a creature (easier to control, more expensive to protect) and more expensive.
Can Obscure be used on the same critter more than once? Is the effect bound to a particular fountain, or will any fountain still in play do?
All that is mentioned in the first post. Yes it can be used more than once on the same critter, and no, it's not bound to the fountain that caused the effect. Any fountain still in play will keep the effect in play.