Simple past tense and past participle of nerf.(verb)
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Use "nerfed" in a sentence
"Trap avoided: this class already got nerfed from the playtest doc where he could cast a large number of 1 minute/level Summon Monster SLAs and could easily boost his eidolon’s AC to the 50s without breaking a sweat."
"And can you tell I just really like writing the word "nerfed"?"
"I like the word "nerfed", though I must confess to being terribly unworthy because I have no idea which vampire series is being referred to."