If you jump up when Ridley has 0 hp and is approximately in this position (right after a swoop)  - https://puu.sh/BoXE4/28d5a9c034.png - you can get him to insta-die on the spot.

See https://milde.no/public/rightside.mp4 and https://milde.no/public/leftside.mp4.

He is coded to do do 10 Lunges before insta-dying. But in certain conditions, the counter is increased once every 2 frames.

ALL of these conditions needs to be true:
- Samus can't be spin jumping
- No powerbombs can be going off 
- Ridley needs to be approximately at the middle of the screen (vertically), with his back towards the wall. Coords: [0x60, 0x100] or [0xC0, 0x100] depending on which way he's facing, with some margin.

ONE of these conditions needs to be true:
- Samus is more then "2 blocks" away from Ridley (horizontally) WHILE Ridley is facing the opposite way 
- Samus is higher than Ridley (Samus' upper body needs to be above the bottom of Ridley's claws, in one testing I did)
- Samus is damage boosting

Generally you would want to go for the "Samus is higher than Ridley" condition. But if you stand in the lava right after he gets to 0 HP (and did a swoop), the "2 blocks away" condition will be used, and he'll always insta-die.


A little bit more technical:

If you look at https://milde.no/public/sm/ridley_diagram.png, the following path is happening repeatedly: B321 -> BAB7 -> B3EC -> B3F8 -> repeat.

B321: Since Ridley has 0 HP, simply don't spin jump and we always get to BAB7 immediately.
BAB7: What we need to hit here, to get back to B321 immediately, is to get to B3EC (Move towards center). The only two real choices is "Ridley is NOT facing Samus, while Samus is more than 2 blocks away from him" and "Ridley is BELOW Samus"
B3EC: This is always immediate
B3F8: If Ridley is already colliding with the coordinate [0xC0, 0x100] or [0x60, 0x100] when we get here, it will move on immediately to B321 again.