Goat format ruling
Chaosrider Gustaph

Card effect (current official text)Once per turn, you can remove from play up to 2 Spell Cards from your Graveyard. This card gains 300 ATK for each card removed, until the end of your opponent's next turn.
Rulings
- You can only activate Chaosrider Gustaph's effect during your MP 1 or 2.
- Chaosrider Gustaph's effect does not target.
- The ATK increase by the effect of "Chaosrider Gustaph" only applies to Spell Cards specifically removed for that effect.
- If the ATK of "Chaosrider Gustaph" is raised by its effect and the following turn, control of "Chaosrider Gustaph" changes to the opponent, the opponent may raise the ATK of "Chaosrider Gustaph" through its effect.
- Q: "Chaosrider Gustaph" works like "Bazoo the Soul Eater," right? If my opponent uses the effect, and I take control of him, I can use the effect to raise his attack by an additional 600, right? A: Correct.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Goat forum — sourced change requests get reviewed.