using Elemental Mastery to guarantee 100% crits on two spells within the batch window is a bug
how do I know this?
cuz Paladins could originally do it as well with Divine Favour but it was nerfed twice over the course of Vanilla:
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Patch 1.11.0: It is no longer possible to cast this immediately after a healing spell and “retroactively” make it a critical hit.
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[Patch 1.7.0] (13-Sep-2005): Paladins can no longer activate Divine Favor on the previously cast healing spell.
https://wowwiki.fandom.com/wiki/Divine_Favor