Effective stacks: $300

Villain: First time I've seen a player of his kind. Complete maniac with highly unusual betsizing. Seen him bet 25$ into 8 dollar uncontested pots and of the sort many times. Seen him limp and call off a short stack($30 dollars in a straddled pot) with K3o. He's in almost every hand and plays postflop very aggressively. Built his stack up to almost $1,000 by getting lucky. Seems high or on some substance by the way he's acting but I'm not too sure...
Relevant hand history (I'm not in the hand): He raised on the button with Q6o, and bet pot on flop, turn and river on a xxKA2 board. Has about $1000 to start

Hero: Switched over recently after and playing TAG style. Sitting around $300

OTTH:
Hero raises to $12 UTG with KK, villain calls in LP, CO and BB call.

Flop($49):
JJ6
Hero checks, villain bets $25, CO BB call, Hero calls.

Turn($100):
3
Hero checks, villain bets $50 in 2 green chips, hero calls

River($200):
A
Hero checks, villain asks how many chips I have left ($200), and he bets $300 and says "this should be enough" with a black and 8 greens.

Hero?

Based on your reads seems like a pretty easy call to me. Seems he doesn't have a boat at least 1/3 of the time which is what you need.

I don't love the speech here but I discount that compared to the other evidence in the hand.

Call. You've see him run bluffs, you know he's aggressive post flop. Way more likely he has a random jack or small pair than the boat IMO. You're calling 200 to win 600? I think you're good 33% of the time here.

Oops didnt proof read my post.. its a 6
so flop is J66

I'm not 100% clear on the action -- do CO and BB call or fold to the flop bet, because it doesn't appear as if they take any action on the turn.

Any reads on CO/BB if they did call that flop bet? Because I'd be inclined to make a big reraise if there's a low likelihood that they'd slowplay a big hand like trips on a FD board like this.

Raise turn. Absolutely call river.

I think moral of the story is you should have raised somewhere along the way, rather than just called with KK against this guy.

I would have led flop for 35, led turn for 100, and put the last 50 in on the river. Yes, shoving the turn is also an option, but if the guy is actually high, he may not realize that calling 100 is basically the same as calling 150.

As played, I think you have to call. You could very easily be behind, but you've seen this guy bluff three streets before (I'm assuming for most or all of his stack).

What is his preflop raising percentage? Nearly always? Only sometimes?
Post flop, is he usually shoveling chips in, usually calling off light, or acting unpredictably?

If he's a true maniac, i.e. raising most hands pre and the betting most of the time on all three streets, there are some significant adjustments you can make to get the most from him.

Are we shoving if V raises flop?

Why did we give up initiative?

If there are only three hearts, two jacks, and an ace on the board, I think it is a trivial fold.

Where we attemping to catch him bluffing the paired board? If so, why didn't we check raise the turn? I am super confused by the checks in this hand. (it looks like the way I would mangle a hand in live play against a maniac.. lol)

Sorry, CO and BB folded too. Villains been super aggro in contested pots, even if he has players behind him. I thought raising would fold out most of his bluffs and only call with better, guess I was being too MUBsy in this spot.

His preflop vpip was nearly 100%, raising around 50%, and limping the rest. He actually tried to limp in after my raise, not realizing I put a bet out preflop. I'm not sure how lightly he stacks off when facing a raise but his aggression factor when there is no action in front of him was significantly high.

Initiative is not really relevant here as we have a value oriented hand. Plus did you read the villain description?

PF: OK

F (49): SPR is ~6. Hmmmm...why no cbet? Even with 4 people in the hand and when the BB checks, I'd fire $30. Is our plan just to call the "Maniac" V down? Only problem now is that the BB is in the hand.

T(124): Uh Oh....flush just got there. So what's our plan? Again is our plan just to call down the "Maniac" V? OK, so BB folds...well that's good. When we call this $50 bet, we must be calling here to call down any river. We must know now we don't beat anything except a pure bluff.

R(224): We've got $213 left. We just spiked the nut flush! Snap Call against this guy even if the board is paired!

Sorry, I stated above that it was the 6, not the 6. So final board is
JJ63A. I butchered this hand by not betting on the flop and following through with my initiative.

Just a question to some of the other posters: why a raise on the turn?

Its high variance to play against maniacs like this, if hes an ATC mega bluffer. I played against a player like this where I called down with third pair on a very large river overbet (like 200bb) and was good. If he truly opens ATC and then relentlessly bluffs at weakness (you checked flop) I think this is a call. But I wouldnt know without seeing more hand histories. Theres usually some method even in their madness. Some maniacs would slowplay trips on this flop and only attack when they have air or weak pairs. Some are more balanced and capitalize on their image when they have something.

AP - you just backdoored the nut flush, why did you call the turn if not to hit this card and get it all in? At this point I think this is a snap call.

If he really is crazy agro preflop, I think this is a great opportunity for you to go for a limp reraise. Your stack is short enough that it doesn't matter that you hand is essentially face up when you do it because you'll collect the pot at that point and move on to the next hand OR the dude may spazz push which is even better.

I think the lack of a c-bet is most surprising. Why didn't you fire that barrel?

There is only one piece of advice for this hand:

BET. THE. FLOP.

Everything that comes after is irrelevant, this was the key moment.

Fwiw I probably fold river because I hate playing poorly and going broke.

I don't fear insanity, I enjoy every moment of it