You were doing Saviour run a.k.a Pacifist run but You get guided by Asriel ghost instead Of Chara's and where your weapon is Chaos Saber...

You were exiting CORE with 20(MAX) LVL due to farming Monster From Ruins cus they were left alive... by sparing them over and over... LVL is basically alternative to LOVE, where you gain it by sparing and not killing and it power you up as Same as LOVE but just method to gain is more Pacifist... However when you get to Judgement Hall/Last Corridor suddenly you see a DustFell Sans... As he looks at you in confusion...

DustFell Sans: Wait... where's Frisk... Forget it... Let's end this...

He then summons Many Gaster Blasters and Sharp bones as Sudden Fight starts... As Asriel Ghost speak to you...

Asriel: His attacks all point at you... It's easy to dodge, despite it being scary due to amount of it... Moving away is enough to dodge... almost all of them...

As you summon Two Chaos Saber and hold them in dual wield... As you also ready to fight...