Rippers are definitely most annoying. It's so easy to die there. I wouldn't mind this high-KO potential if they actually felt rewarding to kill, but unfortunately they don't.
I dread getting these tasks. I do Wyverns though because they're quite quick to do. Thankfully these tasks don't seem that common. Although, I haven't slayed that much recently so that could be why I haven't really noticed their true frequency.
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Even with my blocklist that blocks high weight tasks, I don't get them too often (Edimmus and recently Rune Dragons are all that are on my prefer) - They're not worth blocking really.
Mammoths are great fun to kill and their tusks are around 100k each, granted in 400 kills I've only had 15 of them.
Unslain Bosses - Clan
Don't think I'll do wyverns after I get their key piece. Rippers and Mammoths are the only ones I can see myself killing for non-key reasons. Although this may change over time as I get more annoyed by their lack of loot for increased effort. At some point I think I'll have killed them enough and it won't seem "fun" anymore and just come across as a waste of time lol.
They've really crashed that hard? Yikes. I knew they were far from good enough to gold any sort of value, but damn. I guess staves and bows shouldn't be too far behind, but the low supply may keep them artificially inflated for quite some time as well :l.
Bows are 75m (and actually holding their price, they're apparently > nox for long fights, there's just no long fights), and god knows why staffs are 140m each.