Heathcliff explained to Kirito that he had to engage the system’s assist mod when defending (against Kirito's attack) because he's (Kirito) so fast. But how was he able to automatically access it? I know that he is the GM but we’ve seen that even GMs have to either utter a voice command or navigate through the menu in order to instruct the system.
I think the reason why Heathcliff was able to do so lies in the fact that NerveGear works by scanning the brain wave. It receives input by reading the brain wave as the person equipping it thinks about something. For example, when we talk, the words are formed in our mind and the brain sends pulses to our mouth and voice cord to produce sound matching the words formed. This pulses is what the nerve gear receives as input, and at the same time, prevents the actual organ from receiving it.
It is possible that for his account, he has a feature where he can activate or deactivate game feature simply using his mind. That is, he can command the system by thinking about it. No need for him to think of moving his hands and access the control panel.
The reason is actually simple if you understand a very important explanation and demonstration from Yui, in the anime Epsidode 12, Yui's Heart. To explain what is happening, Asuna and Kirito meet and adopt a young stranger girl who seems alone wandering through a forest, and they choose to take her in and nurse her back to health hoping she would awake from a big collapse in the middle of the forest, as in the episode prior, episode 11, the girl of mountain dew, Kirito and Asuna immediately after witnessing her fall and being passed out automatically have their emergency and game analysis of every possible conceivable reason for her to be there alone, too young for a normal player and the big clue of no cursor which every player always has no matter their circumstance not show. So she of course surprises them with a healthy dose of amnesia when finally awaking, and it's bad enough to basically not have her remember her lifes entire past. Parents, age, the most basic person with amnesia still knows that and she was to Quota asuna like a blank slate, even affecting her vocabulary and her learning of language. But the point to take away is that this situation was a first to give off too many flags that it should have called their suspicion of the icon even harder consering it was made to be a major notification. And it was clearly noted that she had to have barely been playing because of the comments on her gear and the way Kirito mentions she must not have been in any fights. Jumping ahead to conciude the next day they quest together and find a floor boss not expecting one and seeming to Kirito to be likely the highest level boss they've seen so far and krito and asuna were trapped with the option to fight and die or just get killed. Getting nearly a death blow blocking one attack Yui who was hiding comes out, seems to act like a normal human, but then confronts the boss head to head, magically sunnons a sword thats on fire and does a super high jump skull splitter taking it out. We find out she is AI.. AI is a program. Everything that is run in Aincrad has something to run it.. mentions are what the bosses drops,etc etc... Basically everything that makes the world aincrad, it is all controlled by a sydttem a computer system, or you can say an AI. This AI is the famous Cardinal System you hear so much about but don't really get to understand. You find out Yui is an AI, she is given specific privileges as that Pegram and had general Admin access to the system. That's a lot of privileges. So what she did on her own with no need for any assist needs was not mutter words or anything and have a superior weapon be given to her and she gained the immortal object foecedield on demand preventing an attack to touch her yet never made specific sudo instructions to do so. The commander is able to use the system to pick and choose who he wanted to paralyze easily, although it seemed like he used an assistant remote control to help him make changes to his world he made. That should be enough to show that you like both Yui and healthcliff as we learned both uses the system assist mode, which just seems to give them invincibility. and remove it on demand. also as it was the cardinal system that granted those rights, both had Admin access which meant they had control to manipulate the system to do whatever they wanted the cardinal to do. and the final instruction to self destruct and erase the world was an opinion that was one of who knows how many commands are possible. So human or no human (meaning no nerve gear) Both effectively used the cardinal system very effectively to eliminate the problems that they each had to use. They needed to be Admin. And 2mwe find out that the AI Yui can summon weapons and take a direct hit with no damage by having some kinda foecedield. Both seem to have their defense kick in automatically. Only Yui seemed different summoning an item. you do login into the game. heathcliff probably had an admin account. he used privls by using his hand console. he could have like mentioned in other boss battles had it automatically control for him. Yui didn't need any hardwar3 She's a computer. she tells of give Admin privs on day one. apparently you just have to need to know how it works.