Day 7 of the war - Bhishma attacked Shikhandi and Shikhandi was leaving the war, Yudhishtira stopped him saying that Shikhandi VOWED to kill Bhishma in front of Yudhishtira and Drupad. Yudhishtira asked him not to be a man who is unable to fulfill his vow bringing shame to his race and family, Yudhishtira told him that he has nothing to fear as Arjuna will be there to protect him from Bhishma
This one was an important read because Pandavas take vows/oath very seriously, they didn't kill people to uphold these vows, Arjun was ready to kill Yudhishtira to keep his vow
"The high-souled Ajatasatru, angrily addressing Sikhandin in that battle, said these words, 'Thou saidst at that time, in the presence of thy sire, unto me--Even I shall slay Bhishma of high vows with my shafts of the hue of the effulgent sun. Truly do I say this.--Even this was thy oath. That oath of thine thou dost not fulfil inasmuch as thou dost not slay Devavrata in battle. O hero, be not a person of unfulfilled vow. Take care of thy virtue, race, and fame. Behold Bhishma of terrible impetuosity scorching all my troops with his innumerable arrows of fierce energy and destroying everything in a moment like Death himself. With thy bow cut off avoiding the battle, and vanquished by the royal son of Santanu, whither dost thou go, forsaking thy kinsmen and brothers? This doth not become thee. Beholding Bhishma of infinite prowess, and our army routed and flying away, thou art assuredly, O son of Drupada, frightened, since the colour of thy face is pale. Unknown to thee, O hero, Dhananjaya hath engaged in the dreadful battle. Celebrated over the whole world, why O hero, art thou afraid today of Bhishma."
https://www.sacred-texts.com/hin/m06/m06086.htm
1 Then the diadem-decked (Arjuna), excited with wrath, and placing Sikhandin ahead rushed at Bhishma and cut off the latter's bow.
2 Thereupon mighty car-warriors, seven in number, viz., Drona and Kritavarman, and Jayadratha the ruler of the Sindhus, and Bhurisravas, and Sala, and Salya, and Bhagadatta could not brook that act of Arjuna. Inflamed with rage, they rushed at him. Indeed, those mighty car-warriors, invoking into existence celestial weapons, fell with great wrath upon that son of Pandu, and covered him with their arrows. And as they rushed towards Phalguni's car
They rushed towards Arjuna's car, No mention of Shikhandi here
3 Hearing that furious uproar, the mighty car-warriors of the Pandava army rushed forward, O bull of Bharata's race, for protecting Arjuna. They were Satyaki, and Bhimasena, and Dhrishtadyumna of Prishata's race, and both Virata and Drupada, and the Rakshasa Ghatotkacha, and the wrathful Abhimanyu
These people rushed to protect Arjuna from 7 others, again no mention of protecting Shikhandi by these people who was the KEY to defeat Bhishma, Bhishma won't kill Shikhandi but those 7 warriors will, and there goes the only chance of killing Bhishma
^^^
This point was an important one for me to remove the possibility of Bhishma telling them the way to kill him was Shikhandi
After this -
Then the son of Ganga took up another bow that was tougher. That even was cut off by Phalguni with three sharp shafts. Indeed, that chastiser of foes, viz., Arjuna, who was capable of drawing the bow with even his left hand, excited with rage, one after another, cut off all the bows that Bhishma took up. Then Bhishma, whose bows were thus cut off, excited with rage, and licking the corners of his mouth, took up a dart that was capable of riving a hill. In rage he hurled it at Phalguni's car. Beholding its course towards him like the blazing bolt of heaven, the delighter of the Pandavas fixed five sharp broad-headed arrows (on his bow-string). And with those five arrows, O chief of the Bharatas, the angry Arjuna cut off into five fragments that dart hurled from Bhishma's arms. Thus cut off by the angry Arjuna, that dart then fell down like a flash of lightning separated from a mass of clouds. Beholding his dart cut off, Bhishma became filled with rage.
Arjun incapacitated Bhishma by breaking every weapon, he was using, there's a mention of Shikhandi shooting arrows at Bhishma. In this we can't say that Bhishma didn't fight Shikhandi, as he didn't get a chance to do it, also there's one place on day 10 where I read Bhishma attacking Shikhandi, I will look for it
There's alot of repetition after it, Bhishma mentions feminine nature of Shikhandi and says he won't fight anymore but he keeps fighting then after Arjun cut his bows, broke his dart and chariot, Bhishma says he won't fight Arjun after it but again he is coming down from his chariot with a sword to fight but Arjun cut his shield
Desirous of obtaining either death or victory, the son of Ganga then took up a sword and a shield decked with gold. Before, however, he could come down from his car, Arjuna cut off by means of his arrows, that shield into a hundred fragments.
__________
Then that great bowman, Partha, stationed at the head of his troops, broke the centre of the Kuru army. Ourselves then, afraid of Kunti's son Dhananjaya having white steeds attached to his car, and afflicted by him with polished weapons, fled away from the battle. The Sauviras, the Kitavas, the Easterners, the Westerners, the Northerners, the Malavas, the Abhishahas, the Surasenas, the Sivis, the Vasatis, the Salwas, the Sayas, the Trigartas, the Amvashthas, and the Kaikeyas. 1--these and many other illustrious warriors,--afflicted with arrows and pained by their wounds, abandoned Bhishma in that battle while he was fighting with the diadem-decked (Arjuna).
Now look at this, here Arjuna is ahead of everyone, no mention of Shikhandi again, no mention of Arjuna putting Shikhandi ahead of him, Kauravas abandoned Bhishma when he was fighting with Arjun.
Dhritrashtra and Sanjay mention this in their conversation that Bhishma was killed because everyone abandoned him, I will look for it
Thus was thy sire mangled with arrows of keen points by Phalguni in that battle. And then he fell down from his car with his head to the east, a little before sunset, in the very sight of thy sons.
Clearly mentioned that Phalguni (Arjuna's) arrows made Bhishma fall from his car
When Santanu's son Bhishma of mighty energy, who was (regarded as) unslayable, was slain, all of us thought that the destruction of the Kuru king was at hand. 1 Vanquished by Savyasachin, with our foremost heroes slain, and ourselves mangled with sharp arrows, we knew not what to do.
From Drona Parva -
Sanjaya said, 'Beholding the grandsire, viz., the venerable Bhishma, that destroyer of all the Kshatriyas, that hero of righteous soul and immeasurable energy, that great bowman thrown down (from his car) by Savyasachin with his celestial weapons, lying on a bed of arrows, and looking like the vast ocean dried up by mighty winds, the hope of thy
thy sire Bhishma of high vows, that grandsire of the Bharatas thrown down in battle and lying covered with Arjuna's shafts, on a hero's bed.
There are citations saying Shikhandi killed Bhishma aided by Arjuna or protected by Arjuna and there are citations saying Arjuna did it and those have no mention of Shikhandi
Most important point comes from subsequent chapters in Drona Parva where everyone is fearing Arjuna not Shikhandi, Kauravas didn't set out to defeat someone who killed their Commander In Chief.
I came to 3 points -
1 Shikhandi was added to give Bhishma a decent farewell, he didn't die because he couldn't fight, he died because he didn't wish to fight someone from LGBT community
2 Shikhandi and Arjun both were attacking Bhishma, it can't be decided whose arrows killed him
3 It was Shikhandi's vow to kill Bhishma, with the uncertainty of which arrow killed Bhishma they decided Shikhandi did it, otherwise from war chapter, even if I remove Shikhandi, there's absolutely no change as Bhishma surrendered to Arjuna not Shikhandi
Krishna tells Bhishma's mother that Arjun killed Bhishma, I read someone saying that Arjun was born to kill Bhishma or something like that
Note - We discussed it but this keeps coming back so I thought about opening a post to share more information and analyze Bhishma's death