To enable @hardcore command, you must first fulfill two requirements:
Fresh level 1 character
Less than ten minutes of play time (/playtime)
By accepting the quadruple confirmation, your character will be reborn with the following classic FFXI changes:
EXP Rate becomes 1.0x
Run speed becomes 40 (default)
Craft Rate becomes 1.0x
Disables access to most commands, including @mog @lib @leaf @skillup @hunt @shop(all of them) @ah @pw
Disables access to mounts
Disables access to trusts
Hard level capped at 75
Disables access to mythic/relic/empyrean weaponskills upon reaching required combat skill
Disable regen from weaponskills
Disable scaling based on level for /heal
Disable entrance to Abyssea via abyssean maws & teleporter to Abyssea via Joachim
EXP loss is back to 10% per death
The Valhalla quality of life changes:
Signet remains unchanged
Combat skill rate remains 2.5x
Fame rate remains 2.5x
Gil upon monster kills
Special icon that differentiates hardcore from normal players
All outpost warps are available
Explorer Moogles are available