I've been soloing Chukwa on SCH as a 78SCH/RDM for Chukwa's Eggs. Haven't seen a Creed Collar drop, but have seen a couple of Siege Bows.
When you first aggro Chukwa, he goes into his shell and doesn't move. During this period, I used Parsimony+Blizz4, Cryohelices and Bio2s to bring him down. He has some auto-Regen, but it is trivial compared to Aspid. Bio2 pretty much takes care of the Regen. On 2 of my 3 attempts, Chukwa had a huge magic def bonus when in this "initial aggro shell" phase, and Blizz4s were doing ~130, Cryohelices for ~20. On 1 of the 3 attempts, however, he had no discernible magic def during his "initial aggro shell" phase, and Blizz4s were hitting for ~650, Cryohelices for ~100. For future attempts I am just going to assume the "initial aggro shell" phase gives him huge magic def, and this affects kill time significantly, but it's more of an issue solo than in a group.
Once he hits ~85% HP, he uses Mighty Strikes and comes out of his shell and chases you down. During this out-of-shell Mighty Strikes phase, you can continue to nuke him while he's chasing you. His Mighty Strikes+Tortoise Stomp can oneshot you through Stoneskin/Protect4 (did 1200+ dmg), and he seems to be able to Tortoise Stomp regardless of TP. He runs slow, and I never saw the need for Gravity/Bind and didn't bother to test. Once Mighty Strikes wears off, he goes back into his shell and now gains huge magic def, and if you're within casting range, he will start casting WatergaIV/StonegaIV/FloodII/QuakeII which are fairly easy to run away from. 28" is not far enough to avoid the spells, presumably because of his model size, but I found 31" to work; could be less, could be more. While in his shell, you can rest MP (I did it about 33" away to be safe). He will then use Mighty Strikes after some time(~1min+) and chase you again, at which point his huge magic def wears off again and you can nuke him. The bulk of the fight is about getting in as many nukes as possible during his Mighty Strikes phases (when he's susceptible to magic damage). In my experience, I only had enough time for an Alacrity+Blizzard4 and Alacrity+Cryohelix and the occasional Drain/Aspir and kept Bio2 on fulltime. Occasionally I'd have to skip either Blizz4 or Cryohelix because Stratagems don't recharge quickly enough to use 2 every Mighty Strikes phase. With a group, I imagine you'd be able to zerg him with nukes during Mighty Strikes.
There's also the issue of deaggroing him while kiting him. If you're the only group/person going for him, deaggroing him works in your favour because in his deaggroed state, he does not have huge magic def and it's like a free opportunity for doing a full dmg Blizz4. However, if you have competition for him, do watch out for deaggro because it happens quite often, to such a degree that I could exploit the deaggro mechanic to have more chances at doing full dmg Blizz4s to cut down the time required for the kill.
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