User blog comment:FairyRaven/Fairy Tail Chapter 416: Tartarus Arc: Final Part, Review and Commentary/@comment-112.208.8.33-20150119163159

Thank you i totally forgot about frosch dying in a year. I remembered future rouge totally natsu who killed frosch in the manga and anime and natsu was surprised. It is possible that Natsu will turn insane and he will kill frosch. Also, the GMG is a dead giveaway that Tartarus would fail. unless future rouge. Remember: Kyouka surprised to see silver in HUMAN form meaning it is possible he is originally planned as a demon.

After meeting almost all important memebers of tartarus gathering. they are faced with an altar that didn't have an appearance with natsu and co.

Zeref's first appearane he told natsu "end is someone igneel couldn't beat rather he couldn't destroy" something like that.

Zeref told when natsu would meet end he would choose to kill end or not. this line is a bit blurry because end is etherious natsu dragneel.

frosch will be killed someone natsu knows. it obvious from his reaction that he is very surprised that he/she would kill frosch and that would limit who is the murderer.

zeref in tenrou island. answers is in ft zero probably

p.s the monument is an ordinary monument. look for the book cover of vol 13