Questions about Orochi (Big Snake) Escape Prevention + 2 newest achievements

[Armeisen]

IIRC bamboo and magatama are required but I've had a run where the snake still escaped when I had both those items. So was I just missing something else? How do I get him to not escape? This is solo play btw.

The second question is how do you get the two new Oni bosses to show up? Browsing through one of the japanese pinned threads here, I come across a comment about how the person was trying to summon the Oni bosses by having all his NPC party members carry bells. Is this actually the case? Does this mean I need to actually run multiplayer now and pray the group can actually clear Orochi so that I can inherit the bell at the end? Because I have no idea how anyone but Gonbe can clear the game solo.

If this is the case, why would the devs lock achievements behind dead multiplayer content?

[BKo]

I believe it's the bells, and I don't play solo, but I've never seen them appear unless I was on one of the characters who I had saved a bell to already going in (and probably other people also brought saved bells).

[zantomun]

The spear needs to do a certain amount of damage to Orochi, supposedly about 30% of his HP, before the 20% mark or whatever where he runs away. I think a reliable way would be to purposely run out of ammo so that your CPUs only deal weapon damage as long as you can generate enough shields to tank the boss or CC to keep minions away. I don't bother soloing as anyone but Gonbe so just an idea.
The magatama only keeps away certain minions that he spawns like the woman ghosts as far as I know, it's definitely not required to keep him from running.
I commented in your other thread about the Oni bosses.
The bell can be found anywhere in the game. I don't know if someone has to already have it for it to become a normal drop, but they can be found from tsuzura with about the same (or more) drop rate as NUM medals. I've had lobbies where they drop two or three times in my quadrant and no one even wants them anymore lol.

[Armeisen]

hmmm actually informative af. Thank you zantomun.