Harry Potter, exactly what I was thinking. waaaaah

Can i give a level 1 party of 6 this?

most of them are both faster and longer ranged than this monstrosity

.

Absolutely not. 1st off, its challenge rating is a bit high, making it a hard encounter. 2nd off, a hoary of their level has no way 2 reverse petrification, making it a monster capable of perma-killing them. 3rd off, it does an average of 17 damage with its bite, enough to 1-shot anyone who isn’t a raging barbarian. In fact, a raging barbarian can be expected to have 15 hit points and take 12 average damage on a hit, nearly downing them. While this damage number is satisfactory 4 a boss who has only 1 attack per round, it is dangerous as the boss critting would deal 34 damage on average, enough 2 instantly KILL (not render unconscious, actually kill) a fighter on full HP. In fact, the aforementioned raging barbarian, if on full HP, would take a whopping 24 damage, instantly killing them if they have 0-9 health and downing them otherwise. Now imagine this with a fighter or monk, the former having 13 max HP and 29.5 effective HP and the latter 11 max HP. Both of them fall anytime they get hit, although the fighter can recover somewhat effectively they need outside intervention 2 get them back 2 fighting shape. In fact, the fighter and monk will almost certainly be insta-killed on a crit, unless they get super lucky. This is made worse, as the average bite attack will insta-kill the fighter if at 0-4 HP and the monk if at 0-6 HP, which they will almost certainly be at after getting hit once.

However this can be salvaged.

Step 1: kiting is unfun. The party should not encounter this thing in a big, open space where they can kite it 2 death. They should fight in in close quarters underground where they can retreat but must otherwise engage it in melee. 

Step 2: no insta-kills: 1st off, due 2 the low HP of the party, remove critting on Nat 20s until they are lv2. Next, give a way 2 remove petrification. If somebody took alchemists supplies proficiency, tell them that they can make an Elixer from the monsters gullet that can save their petrified party members. Otherwise, have everybody roll an intelligence check with the apropriate skill afterwards, with whoever gets the highest score realising that the basilisks saliva can be used 2 unpetrify people.

step 3: spreading out the damage: if you like, how about ensuring that the damage s a little bit more spread out? Taking something from a 3rd party book, why not decouple the poison damage from the bite and instead make it a reaction where when the baisiliks takes damage from a creature within 5ft it can force them 2 make a dc12 dexterity save or take 7 (2d6) poison damage?

So how would this interact with Blindsight?

I know this post is almost 5 years old by now, but for anyone reading this, basilisk oil can revert a petrified creature to its original form. You can harvest basilisk oil from a basilisk, living or dead. I would recommend having a character make a nature check to recall the information, and then a medicine check to harvest it properly.

Quote from Immortalhonyebadger >>

How can this be a challenge rating three creature? It deals not just 2d6 damage on a bite, but also 2d6 poison damage, has 52 hit points, and possibly can permanently turn you to stone if you fail your save! I would think that it should at least be a challenge rating of 5 or 6, especially with the way that it can instantly kill player characters. 

Look at the table and instructions on DMG 274.  The basilisk has a DPR of 17 (yes, the bite attack is strong, but it only gets one per round).  With a to-hit of +5, that means an offensive CR of 3.  Meanwhile, 52 HP with 15 AC means a defensive CR of 1.  To get the overall CR, average the offensive and defensive and you get 2.  Now, that does not account for its petrifying gaze, but I figure that's what takes it from 2 to 3.  (And BTW, it doesn't instantly kill characters, it petrifies them.)

The gaze is a bit weird to account for in the CR.  While it could get very hairy if players don't think to avert their gaze, it is fairly easily circumvent it if they do.  So perhaps the best way to account for it is to assume all attacks against it will have disadvantage, as the players will be effectively blind against it as they avert their gaze.  Disadvantage is roughly equivalent to a -5 on the attack roll, or a +5 to the basilisk's AC.  That bumps the defensive CR up a couple of notches to 3.  So, now your overall CR is 3, just like the stat block says.

Any system that boils monster difficulty down to a single number is going to have trouble accounting for everything, especially situational factors, but also special features like this one that aren't strictly just damage or defense.  So, CR and the encounter difficulty calculations on DMG 82 that make use of CR are just starting points.  You do still have to consider the particular party and the particular situation of the encounter.  If you think your party is not going to figure out (or haven't been told) to avert their gaze, and they lack ready means to restore petrified creatures, then yes, this is probably going to feel like more than a CR 3 in actual play.

Also don't forget the save DC for the petrification is 12, which is the lowest spell save DC on the CR table. And you get 2 attempts before having to determine your pose for eternity as a stone statue.

Very carefully.

how the hell is the thing on that picture a basilisk

no

Yeah... should create FLUFFY!!!!!!

i said the saliva is able to return a creature back to its form if harvested properly