Double straddle gets weird action and runout

1/3/6/12 NLHE.

We're single and or double straddling every hand. The game is playing soft with large sizes being bet and (usually) cold called.

BTN - East indian drooler. Can't play poker. Completely face up. Buys in 100 on repeat and just calls it off over and over. Betting range is 2 pair +. 115$.

BB - Unknown MAWG who we've seen be very LP and sticky post. VPIP about 80%. 840$.

--- We cover BB's 840$

H double straddles 12, folds to BTN who limps, SB folds, BB calls, UTG calls, H sees A♠ K♦ and makes it 100, BTN and BB call. 3-ways 2nd to act.

Flop 320 - 9♦ 8♣ 4♥

BB checks, H 125, BTN AI 15, BB calls

Turn 365 Main, 220 Side - 8♥

BB checks, H checks

River 365/220 - 9♠

BB checks with 615 back...