L Mammoth Tusk Piece - what's the best place to farm?

Tittle says it all.

Legend episode 2, there is a stage where you save the trapped yukis. I cant remeber the exact time, but you get like 15 minutes to save 10 of them or something. In this stage, you can repeatedly go back and forth within the mammoth area to kill them. It is the fastest way because other stage have a limited number of them where as this stage it regenerates indefinitely until you fail to safe 10 yukis or something.

2-3L second from the left; top row;
It's worty to kill 1 of that assasins - then you get owned at 2:30 instead of 4:50.

It's 3-7 tusk pieces per run so it's 120-150min of pure farming.

I have 21 tusk pieces now.... sigh...

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It sucks, yeah. ;3