From the script:

Suddenly the mood in the room takes on a bit of an ominous vibe as the tapestry in front of her comes to life and the Good and Evil Alicorns from the fabric grow and become animated.

The two Alicorns from the tapestry sort of battle with each other around Sunny as the Mysterious Voice tells a story about the responsibility that comes with being an Alicorn,

MYSTERIOUS VOICE
Since the beginning, Alicorns have been the rarest of creatures. Given incredible power - their potential is limited only by their imaginations. Over the years, some have used their power to spread goodness and hope and to protect ponykind...

The “good” Alicorn in the room, climbs a fictional mountain and once at the top shines out a light of goodness from her heart, filling the room with an incredible glow of warmth.