Concepts here that don't come up too often so I figured I'd stir the tank.

HJ: $18,000
CO (Hero): $12,000
BTN: $15,000
SB: covers
BB: covers
Straddle: $6,000

3 folds, HJ raises to $175, Hero reraises in CO to $425 with K Q, 4 folds, HJ calls $250

Flop ($935): K Q 8
HJ checks, Hero bets $600, HJ calls $600

Turn ($2,135): J
HJ checks, Hero checks

River ($2,135): J
HJ bets $1,600

Fold, call, or shove?

I think fold is usually best pre. I find a call if there's a fish in the blinds, and 3-bet only if I think the HJ is opening excessively. As to the size, I don't like it. You need fold equity to make money with that 3-bet, and your stronger hands probably want to get more value.

On the turn I think you can probably find a bet. There are a lot of hands to get protection and value from, and probably betting turn is your best chance to get a bet in good with this hand. Your hand is too strong to confidently fold rivers, and too weak to confidently call rivers. As played, I fold. I hate raising when you can't rep KK QQ.

^ fold KQo pre IP to a HJ open (assuming 25/50)?

3b is fine but this sizing indicates a likely mtt button clicker

Any reads?

Without, pre seems ambitious and river seems like a fold

Pre is a good spot but executed rly bad
Turn is bad
River is prty obvious

+1

I should have clarified some factors in the initial posting. Straddler is a big fish, aggressive preflop and passive postflop, who will cold flat 3-bets with various junk, not everything, but certainly any suited ace or connector here. HJ is indeed opening wide to isolate him. Blinds are professionals and I deem them aware that if they 3bet they will be sandwitched postflop between his deep stack and the fish's shallow one; flops will often go check~fish check~HJ bet~tough spot; cbet~fish call~HJ call~tough spot; or cbet~fish call~HJ squeeze~. All these lines seem massively unprofitable. So they are probably 3betting very seldom, possibly 0%.

BTN is also professional and will squeeze a huge amount, for the opposite reasons, every spot postflop will be excellent for him to play (check~check~cbet~fish calls~HJ tough spot). So let's think how all this information shall add up to a good preflop strat in CO.