The ATK of this card is the number of Monster Cards in your Graveyard x 300.
Rulings
Individual Card FAQs
If you equip "Chaos Necromancer" with "Axe of Despair" and have 5 monsters in your Graveyard, the ATK of "Chaos Necromancer" is 2500 (1500 + 1000).
If "Chaos Necromancer" is equipped with "Megamorph", its ATK is zero, but if "Megamorph" leaves play, recalculate the ATK of "Chaos Necromancer" using his effect.
If "Shield & Sword" is activated, it reverses the original ATK & DEF of "Chaos Necromancer", which are both zero, then "Chaos Necromancer"'s effect is applied and his ATK will be 300 x the number of monsters in your Graveyard, and DEF zero.
DARK|
Level 1|[ Fiend / Effect ]
ATK 0|
DEF 0