Most people use Drobot because they believe he can move the fastest. He can also attack while moving which is a huge plus. People also use Ignitor for boss fights because he can do lots of damage in a short amount of time. We have not thoroughly tested all of the characters though, and most people just use whichever skylander they think is the fastest. (I currently use Ghost Roaster). We need to do more testing to find out exactly which skylander is the most optimal to use in speedruns. We can talk about this more in the discord if you'd like.
IMHO:
In Speed Terms throughout the run: Go with either Bash or Zap In Boss Terms (Especially Kaos): Go with Drobot or Trigger Happy
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