Life Crystal

There is no reason to carry these around. Any world holds several times more than one character can ever consume, so the only thing you give up by using one on the spot is the option to bank it, and there is nothing worth banking it for. The heart lands immediately and the crystal tops your health up as it goes, which is often enough to rescue a cave run that has gone badly.

They sit embedded in stone anywhere from the underground layer downward, placed when the world is generated rather than dropped by anything, and they are thin on the ground rather than common. Two places never hold a single one: the Dungeon and the Underworld. Do not spend an afternoon sweeping either. Fishing is the other supply line, since Golden Crates and Titanium Crates both turn one up from time to time, which is a fair way for a player who hates caving to catch up on health.

A Spelunker Potion highlights them through solid rock and turns a hunt into a walk. The underground jungle is the quickest sweep because its caverns are huge and run into each other, though it is also the most likely place to get you killed at that point in a run. Ice caves and glowing mushroom caves cover less ground per minute and are far calmer. Worlds occasionally fail to place one or two, so even an exhaustive dig comes up a little short of the theoretical count.

Each character can only absorb a fixed number of them, and once you hit that limit the game refuses to consume any more, so a stray click costs you nothing. Everything past that has to come from Life Fruit, and only once the world has turned hard, which makes the crystal cap your real health ceiling for the entire first half of a run. A few events key off maximum health thresholds rather than off bosses beaten, so rushing to the cap early does change what the world starts throwing at you.

Extras sell for a decent sum, but crafting usually beats that. They become Heart Lanterns, and a lantern hung over an arena is permanent regeneration you never have to think about again. Later recipes want them too, the Panic Necklace among them, so keeping a handful in a chest rather than dumping the lot on a merchant tends to pay off.

They are the health half of a pair with Mana Crystals. The placed sprite is also one of the last in the game still openly drawn out of the plain stone texture. Almost everything else that borrowed from it, old ore included, was redrawn years ago.