Who killed Duryodhana in Mahabharata

What are the three mistakes Duryodhana made in the Kurukshetra war?

There was no such event between Duryodhana & Krishna where 3 fingers were lifted.

After being stuck with broken thighs, Duryodhana angrily complained to Krishna about how his deception tactics had cost the lives of great auto warriors like Bhishma, Drona, Karna, Jayadratha, etc.
Krishna responded by counting all the mishaps attempted by Duryodhana & Co. such as poisoning Bhima, burning her alive in Lac's house, insulting Draupadi, deceiving Yudhishtira of his kingdom, and so on.

Duryodhana, holding on to his own POV, curses Krishna and this is followed by heavenly beings who praise Duryodhana with roars and flowers.

Duryodhana said: "... Who is as happy there as I am! ... With all my well-wishers and my younger brothers, I go to Heaven ... As for you, with your intentions that are unreached and torn grief, live in this unhappy world! "

Sanjaya continued, “At the conclusion of these words of the intelligent king of the Kurus, a thick shower of fragrant flowers fell from the sky. The Gandharvas played many charming musical instruments. The Apsaras sang the glory of King Duryodhana in a choir. The Siddhas made a loud sound, "Praise be to King Duryodhana!" A fragrant and delicious breeze blew on each side. All quarters became clear and the firmament looked blue like the lapis lazuli. When the Pandavas, under the guidance of Vasudeva, saw these extraordinarily wonderful things and worship offered to Duryodhana, they were ashamed.[Shalya Parva, section 61]

It looks like an anti-climax, but Krishna handled the situation by telling PAndava-s that whatever they did under his command was the only way to win the war and that was fair in this context. They later left the place.

Out of the desire to do you good, I have repeatedly used my powers of illusion and killed them in combat by various means. If I hadn't taken such deceitful paths in battle, victory would never have been yours, neither the kingdom nor the wealth! ... You shouldn't take to heart that your enemy was fraudulently killed. When the number of enemies grows large, the destruction should be done by invention and means. The gods themselves went the same way in killing the asuras. In this way, what has been trodden by the gods can be trodden by all. We have been crowned with success. It is evening.We'd better go to our tents. ... all those kings who had weapons that looked like spiked clubs, then went to their tents , full of joy and blow their clams on their way. [Shalya Parva, section 62]