Wizkids Rules!

White Lantern Sinestro reaads "While White Lantern Sinestro is active, when your opponent rolls energy faces with multiple energy, they must immediately spin those dice down to single energy faces if possible. (E)"

If I have a White Lantern Sinestro active, does he prevent any Energize effects from triggering for my opponent, in any and all steps, or does he simply spin a double energy to a single after the Energize effect triggers?

When Sinestro is active, his ability is already in the queue. Therefore, your opponent must spin any Character die with a double energy face to a single energy face before any subsequent abilities are resolved. Even though the Energize ability triggered, thus entering the queue, Sinestro’s ability must be applied before the Energize ability is resolved.

The result would be the resolution of the Energize ability, but you would have only one energy, instead of two from the double energy face, to spend.