User blog comment:Miskos3/Fairy Tail Episode 253: Tartaros arc: Silver Memories, Review/@comment-5303512-20151004133550/@comment-2214433-20151004150824

The following may contain spoilers. Proceed with caution.

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Generally, if you are an anime only viewer, usually, spoilers in the opening won't mean much because you won't have any idea on what exactly they mean. Like the clock going one minute back in 16th OP = aka Ultear's spell. So in sense, it's indeed just a teaser. However, we have blatant spoilers like Acno/Igneel appearing or Lumen Histoire and that imo destroys the experience. I remember when the chapter with Acnologia attacking Tartaros came out and many of us were in the chat back then, the reactions were quite something and everyone was like wtf. That's what made his appearance great, because we haven't seen him since he blew up Tenrou Island.

tl;dr there's a difference between teaser-like spoilers and blown up major reveals being shown in the opening.