Undyne is the third major battle of Undertale, ... She'll then fire spears and arrows at you from various directions, and you need to deflect them by facing in the appropriate direction.

Suddenly you'll be attacked by a spear, and Undyne will appear. This will enter you into a battle with her where you need to dodge the spears in both combat screens and along the jetty.

Her battle introduces a new mechanic as well, turning you green and having you defend against a flurry of spears from all directions. If you've reset before, Undyne's attacks grow gentler over time.

Here's how to beat Undyne the Undying in Undertale. This fearsome foe boasts bullets and spears that are tricky to dodge. ... If you aren’t careful, she’ll manage to skewer you with her spears.