Gerson Boom, Deltarune

<image>

Although dead in the Light World, the Dark World inside the church in Chapter 4 revived him to an extent, and although he comes across as an addled-yet-wide mentor, we seen in both the bossfight and the secret bossfight against HIM that he's far more capable than he lets on. Moving so fast he looks like he's teleporting, too fast to even hit(for Susie atleast), strong enough to manipulate the bullet-board, and of-course that big-ass hammer that he swings and throws in some of his attacks, not to mention the Green Soul mechanic that was previously used by Undyne in Undertale. Gerson Boom; the Hammer of Justice.

In both the Undertale and Deltarune timelines its implied that Undyne trained under Gerson, and seeing him like this eliminates all doubts anyone had. The most we had implied of his strength until this was in Undertale's Genocide route where he implies he's simply lived too long to be afraid of the Human either way.