Some points to consider

• Encountered Saber the same way as Shirou did in the game.
• Strong possibility that Avalon was never removed.
• Was unable to "free" Saber.
• Had a special relationship with Ilya. Probably guilt?
• Did not necessarily have a sexual relationship with either Saber or Rin.
• First time he projected a weapon, he screwed up one of his arms.
• Pendant is void of maryoku unlike the pendant existing in the present.
• Possibly a product of a timeline where Rin's Servant was a different Archer.
• Had an unpleasant experience in England involving a bridge and the Thames.
• Encountered Gungnir at some point (either that or embedded knowledge through summonings).
• Stuck in a situation where he needed a miracle to save less than a hundred lives. Contract with the world was made at this point.
• Contract with the world granted him physical augmentation in addition.
• Killed for starting a war by a person that he had saved (who also happened to be the one who started it).

　 　 _, ,_　　 なんなんですか？
　　(;ﾟдﾟ)　　ここ、どこですか？
　　　ﾚV）　　 なんであたし
　　　 <<　　　貼られたんですか？