Ace being present in the world results in a multiple changes to the achieveable endings, most are minor.
The Flawed Pacifiist:
Ace is absent from the both of the flawed pacifist endings. He does not take part in either phone call, nor is he mentioned by the other characters.
Again Ace is goes unmentioned in the betrayed Undyne phone call.
The dog ending:
No change needed.
Undyne is alive (Usurper Undyne):
- *ace stayed behind, he's got my old position as the snowdin sentry. i don't think he likes tori very much. sometimes we talk through the door
- (if Papyrus is dead) *it's good to hear a familiar voice, you know?
- (if Papyrus is alive) *pap keeps wanting me to let him in out of the cold while we talk but ace won't walk through. he heard tori talking about him once... i don't think he liked what she had to say.
Undyne is dead:
The ending starts the same but when it gets to Toriel being exiled and Sans/the brothers going with her it goes into...
- *ace is in charge now. he said that if any human came through the door, they would be killed on sight unless either me or tori went with them. if we take responibilty for the the human's actions as they went through the underground then he'd be fine with them there.
- (if Papyrus is alive) *oh and pap obviously, he can escort the human too in theory.
- *he didn't just let tori leave though. he got every monster that had lost a family member to you and forced her to face them, it was a little harsh but... atleast now she knows why he made that decision.
- (if Papyrus is dead) *it was... really hard to tell her what happened to my little bro...
The ending then continues as normal.
Papyrus is alive:
- (after revealing his own job title) *THAT'S A WAY BETTER POSITION THAN CAPTAIN, RIGHT ACE?
- *Considering the fact that I haven't slept in the past three days... Yes it is a way better job than mine.
Papyrus is dead:
- (at the end of call) *and with ace as her captain... i'd be nervous if i were you.
- *i haven't seen ace in a while actually... i wonder where he ran off to.
- ACE MAKES SURE NONE OF THE HUMANS CHEAT ON THE PUZZLES!
- *essentially he's the captain of what royal guard we have left and is kinda our personal bodyguard.
Becomes 'Lord Protector Ace'
- *things have changed rather a lot here. the first thing ace did was change the name of new home, it's called sanctuary now. he wanted people to start thinking differently about us being trapped here. you storming through killing the king, our most powerful warrior, a human killing robot and... he didn't find it hard to convince everyone that we were far safer down here.
- *'that human was just a child, imagine what a group of adults could do, who do you have left to lose'...
- *he put up posters 'safer hidden'... the next thing he did was demand all the golden flowers be brought to him and destroyed.
- (if the human killed Flowey) *he said that it was to clear out reminders of asgore... i don't know how much i believe that.
- (If Flowey was spared) *he seemed to be looking for one in particular, but i didn't ask. i remember him suddenly relaxing one day though... maybe he found it.
- *then he went to the ruins, right to the far side of it and set up spikes directly below that hole. if any humans fall, i doubt they'll survive the landing. and even if they do he tore up the panels for the puzzle, 'brave ones, foolish ones. both walk not the middle road', you know it right? that door is closed forever now. everyone is a little less scared now. he used a fear campaign to get everyone to give up their only chnace of freedom so they wouldn't have to be scared anymore. he kept that fear in everyone's hearts until sealing that door. i would probably have a problem with this is we didn't know it wasn't forever.
The Genocide run
The standard Genocide run as seen in the game is impossible in Akintale. To achieve such a run, Sans and Papyrus must both be killed very earily in the run. Chara would murder the human after killing Flowey.
The True Pacifist
The TP run has different dialogue to the in game version even before Ace arrives. Frisk then takes control of the body when they leave the underground. They and Chara share control fo the body if a genocide run has been completed.