When they pierced the sky, they found there was a gravity invertion, and they had trouble with getting from space to space. Allan went through, and wound up on his back in the black grass - which then moved.
The old man was an undead unicorn - it's horn split into blades.
The old Thing that had not yet become was a geoglyph that was an angel. It was under a pool, and hard to see through the movement of the water. It was carved on a standing stone - and Xavier allowed it to ride him into the world so it could become.
After gathering the angel, the space began to collapse, and they rushed to get out.