Solar Tablet Fragment

Stack enough of them and you get a tablet that starts a Solar Eclipse whenever you want one. That is the appeal. The eclipse drops some of the best gear available at this point in a run, and waiting for one to roll around by itself is slow and unpredictable. Being able to trigger them back to back turns a rare weather event into a farm you control.

Almost every chest in the jungle temple has some, and the lizards and snakes patrolling it drop them as well, so a full clear normally leaves you with more than one tablet worth. If you run out later, the enemies keep respawning, so a short trip back in tops you up without needing to find unopened chests.

There are ways in without a key, and this is the item most people go looking for them over. Temple brick wall sometimes generates outside the door, and standing in front of it lets the temple enemies spawn where you can safely kill them. In the Remix and Zenith seeds that effect is much stronger and those enemies override everything else. Failing that, a weapon that shoots through blocks can bait one into hopping through the door at you, and hammered platforms let you hoik yourself past it. All of this puts you inside a place built for a later point in the game, so bring the gear for it.