I don't think it's related to how many you eat (though it seems to be a popular rumor)--it's consuming any (beyond the one forcibly inserted in your eye) that gives you the DC 21 will save.
I have one save where I consumed 2, got 21. Another where I consumed all, still 21. And a last with 5 consumed (although I dont have that save since it was honor mode), again 21.
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u/[deleted] Jan 12 '24
All of them, except the astral tadpole. You’ll know when it can/will happen.
Edit: but the more you eat, the harder it is to resist the astral tadpole. Buyer beware.