Goat format ruling
Dark Jeroid

Card effect (current official text)If this card is Summoned: Target 1 face-up monster on the field; it loses 800 ATK.
Rulings
- If Dark Jeroid is the only monster on the field when it is Summoned, it reduces its own ATK.
- The ATK cannot go below zero.
- Dark Jeroid’s effect is Targeting.
- If "Dark Jeroid" is the only face-up monster when "Dark Jeroid" is Summoned, "Dark Jeroid" must target itself for its effect.
- "Dark Jeroid" only gets its effect when it is Normal Summoned, Flip Summoned, or Special Summoned. It does not get its effect when it is Flipped.
- "Dark Jeroid" does not get its effect if Flipped as a result of an Effect or as a result of Battle.
- If the monster affected by "Dark Jeroid" is turned face-down or leaves the field, the effect of "Dark Jeroid" disappears.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Goat forum — sourced change requests get reviewed.