Japanese Mispronunciations/Sun Deer
Joe intentionally pronounces various Japanese words wrong to annoy the weebs in his audience. One of these words is "tsundere", (ツンデレ, pronounced [t͡sɯndeɾe] [Soon-dare-ay]) which he pronouonces as "sun deer" instead.[1]
This is a Joeism
When Joe says this, it's not a reference to any stream. It's just something he says sometimes.
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“Joseph Anderson Channel Two” video: “Undertale First Blind Full Playthrough” at 00:56:43.