The Basilisk is one of two monsters added in SLASH'EM that share the cockatrice's petrification attacks. A basilisk is capable of killing you in the same way a cockatrice is; touching a living or deceased basilisk with an exposed part of your body is instadeath, and the basilisk causes delayed petrification in the same manner as a cockatrice. See the article on the cockatrice for specifics of petrification.
A basilisk is more dangerous than a cockatrice, as it has a higher level and thus more hit points, and is also faster.
The basilisk is more dangerous than a cockatrice, but is still slow and relatively easy to hit. Ranged or magical attacks are advisable.
The corpse of a basilisk can be used as a weapon, but weighs too much for it to be effective.
A basilisk weighs the same as a human and is considered a strong monster, making them superior polymorph forms for travel than a cockatrice or asphynx. Unlike the other two, polymorphing into a basilisk will not severely decrease your carrying capacity, making it more suitable for extended periods of staying polymorphed. Female characters can also polymorph into a basilisk to lay eggs, either to hatch into tame basilisks or to use as a weapon.
In Slash'EM Extended, eating a basilisk corpse can increase a player's intelligence by 1 point (50% chance). Trying to do this without stoning resistance leads to YASD, though, even considering that eating a stoning monster in this variant is merely a delayed instadeath. This is because eating a basilisk takes about 30 turns but the turns-to-live timer for delayed stoning starts out at 7, so while the player is still eating the corpse, he will already be a statue before being able to finish eating.
The basilisk is closely related to the Cockatrice. The exact meaning of basilisk/cockatrice is a bit unclear, sometimes they are used as synonyms, other times a basilisk is a different monster. This is why they share the same encyclopedia entry.
The basilisk is alleged to be incubated by a rooster from the egg of a serpent or toad. For the Cockatrice it's the reverse. A rooster's egg incubated by a serpent or toad. Yolkless eggs, were traditionally believed to have been laid by roosters.
The traditional basilisk/Cockatrice is simply deadly. The stoning attack property, comes from D&D.
Like the Cockatrice, it basically resembles a rooster with a reptilian tail and sometimes bat wings. This is why the basilisk is represented by the reptile symbol ":".
Once in a great while, when the positions of the stars are
just right, a seven-year-old rooster will lay an egg. Then,
along will come a snake, to coil around the egg, or a toad,
to squat upon the egg, keeping it warm and helping it to
hatch. When it hatches, out comes a creature called basilisk,
or cockatrice, the most deadly of all creatures. A single
glance from its yellow, piercing toad's eyes will kill both
man and beast. Its power of destruction is said to be so
great that sometimes simply to hear its hiss can prove fatal.
Its breath is so venomous that it causes all vegetation
There is, however, one creature which can withstand the
basilisk's deadly gaze, and this is the weasel. No one knows
why this is so, but although the fierce weasel can slay the
basilisk, it will itself be killed in the struggle. Perhaps
the weasel knows the basilisk's fatal weakness: if it ever
sees its own reflection in a mirror it will perish instantly.
But even a dead basilisk is dangerous, for it is said that
merely touching its lifeless body can cause a person to
sicken and die.
and other sources ]