The Ultimate Alchemy is an important element of Sburb. Its purpose is probably to create a new , or alternatively the planets or life in the universe.
The session's forge may be where it is performed. A fully-prototyped Battlefield . The Ultimate Alchemy requires an extreme amount of grist, which apparently can only be obtained by killing the Denizens.
Terezi suggests that it may be possible to use the grist obtained from the Denizens' death in regular alchemy , which suggests that the grist dropped is all of regularly collectible types.
Vriska has , presumably part of the Ultimate Alchemy: the players must build their houses up to Skaia, grist rigs must be deployed upon each player's fully-built house in order to disperse their planets' grist hoards into Skaia, and then somebody must light the forge (although it is possible that this last requirement is unique to the B2 session; as the Genesis Tadpole , its lighting may be in order to release it and send it into Skaia via explosive volcanism, although this is just speculation). The grist serves as nutrients to mature the Genesis Frog. After this, players can claim the Ultimate Reward.
Assuming a session has a player with Timetables and enemies infinitely (re)spawn (or can be killed repeatedly without stealing grist from a future kill somehow, generated by the players without losing more grist than they drop, etc.), it might be possible to gather enough grist for The Ultimate Alchemy through mind-numbing grinding.