It's one of her chat emotes, it's just "Imagine the smell" (of Tiffa from ff7 and such). She drew all her emotes on streams and they're really good.
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What I like is that they look very distinct at emote size. Many, many, many (near all) vtubers have these cute emotes that look alright at full drawing size but all look almost the same or unintelligible at emote size when actually used in chat. The green thing with light sticks is her pet hermit crab Beanut.
As for for why the smell and the wtf emotes are stickers here.....because it's funny? I don't know, I'd sure make use of the malding and heart ones if we had them.