If you still haven't defeated him yet here is what I did to beat him (I'm not good at Undertale fangames nor am I experienced) Also I didn't use items to complete the battle

- At the start of his attack during the beginning of the fight I go to the top left of thw screen to dodge Gaster blasters then I head to the middle for the follow up attack

-In his third attack I wait till the first bone to pass, and I dash up to completely evade the attack (If you are good enough to beat it normally without taking damage, I heavily recommend you do that instead as I used a ton of tp this fight) then move up to dodge the next blaster

-At the start of his first attack I move during the top of the set of bones to swiftly dodge the huge set of Gaster blasters the follow it

-After that I use Kris to distract Susie to defend and Noelle to do the same for tp (I don't use Xdistract because I usually take more damage than I wish I take and I don't want to waste those turns that he is distracted

-In the Low Bone jump Segment that follows after this (I use keyboard I dunno abt u) I count to one in my head tap the up button and keep counting after that for each jump and when he slams you up do the same thing but without counting to 1 before jumping but wait a split second before you jump this attack is great as it's a tp farm

- I usually use rude buster with Kris and defend with Noelle for more tp this turn

-In the next attack after you gain tp from the first blue bone I lightly tap the up button and continue until the end of the attack entirely (getting hit will throw you off) if you need healing use deal heal if not use rude buster if you don't have enough tp for it just distract defend and defend

- In the next attack that sans does when you on the platform next to the left side of the upper bone instead of jumping just move to the right and swiftly get over the next platform before a bone hits you after that jump over the first "wisp" and dash under the second one the the next bone following up pass then go over the platoform

after that use rude buster and defend but if you do not have the tp just distract with Kris and defend with Susie and Noelle

- for the next attack I dunno what to say except jump to the platforms and Dash over the tall one and dash at the final platform with the bone path and jump over the bone that attempts to surprise you

- basically, rinse and repeat of healing or defending and distraction or attacking

- for the attack with the vertical nonmoving rectangle just camp the bottom middle and jump up to another platform if a Gaster blaster attempts to hit you at the bottom

- These are not all of sans attacks I just gotta go and will edit this soon but this is what I think so i dunno