Why didn't Kotomine just use his awesome fighting skills here?
Because he thought he was dealing with just a regular kid.
Because they had to save they for the grand finale.
Because his awesome fighting skills were fabricated for Fate/Zero's plot.
actually he s pretty tough in heaven's feel.
Did you not read HF?
Sure I did. It's not like it's difficult to fight a kid who is literally turning into swords.
He still didn't do anything after Shirou broke free of the curse.
He was taken by surprise. Happens all the time.
The awesome fighting skills were fabricated for HF's plot.
Fate was the first route Nasu wrote. He hadn't fleshed out all the characters yet at that point, and only later (when writing HF) decided that Kotomine needs to be physically hot shit. This is also the reason why Rin is so slutty in Fate and so pure in UBW, he hadn't yet decided on her character either.
He got careless disease from the Goldie
Shiro win beause of the pot armor, that's all
I don't know what's a pot armor but I want one
Why do that when you can just throw mud at the ginger and let him die of SUFFERING