TCG Rulings

• This card targets 1 face-up monster on the field. ^[1]

• You can activate this card during the Damage Step, before damage calculation. ^[1]

• If the monster you target has less than 800 ATK, its ATK becomes 0 and it will be unaffected by the effects of other Spell/Trap Cards. ^[1]

• "Emobidment of Apophis ^[sic]" will be unaffected by "Trap Stun" and similar cards while it is affected by "Forbidden Lance". ^[1]

• If you use "Forbidden Lance" on a monster being affected by "Shrink", the ATK will be the halved original value minus 800. ^[1]

OCG Rulings

• If "Machine Duplication" targets a Machine-Type monster with <500 ATK that has been affected by "Forbidden Lance", then you can still Special Summon monsters with the same name as the Machine-Type monster.^[2]

References

1. ↑ ^{1.0 1.1 1.2 1.3 1.4} Konami Gameplay FAQ: Storm of Ragnarok -- Card Rulings (Version 1.0)
2. ↑ Konami OCG FAQ: With the effect of "Machine Duplication", can you Special Summon monsters with the same name as a monster affected by "Forbidden Lance"?