Minato was almost invincible!!!
In his appearences in the manga
1. Fought a group of shinobis,trying to kidnap kushina, in his childhood. Defeated all of them. Wasn't shown to get hurt.
2. Wiped out an entire enemy platoon in in an instant. Wasn't hurt. Shown when he reunited with kakashi n rin.
3. Fought A n bee alone. Came out unscathed. Almost forced A to wet his pants.
4. Fought obito. Forced him to flee. In the process, didn't even get hit once.
5. Fought kyuubi. Wasn't hurt till the very end when he decided to sacrifice himself for the sake of the village( which I think was the sole way for kishi to have killed Minato given his abilities).
The only time when he got injured was while protecting naruto from kyuubi and in the process getting pierced by his claw, all this when he had decided his fate.
So, think he was the hardest shinobi to kill. And almost invincible.