Goat format ruling
Magical Marionette

Card effect (current official text)Each time a Spell Card is activated, place 1 Spell Counter on this card when that Spell Card resolves. This card gains 200 ATK for each Spell Counter on it. You can remove 2 Spell Counters from this card, then target 1 monster on the field; destroy that target.
Rulings
- There is no limit to the number of Spell Counters you can have on Magical Marionette.
- Removing Spell Counters from Magical Marionette to use its effect is a cost.
- You can use Magical Marionette's effect multiple times in the same turn, as long as you have enough Spell Counters to pay the cost.
- You can destroy Magical Marionette with its own effect.
- If you activate a Spell Card, and your opponent chains Call of the Haunted to Special Summon Magical Marionette, Magical Marionette does not get a Spell Counter for that Spell Card because Magical Marionette must be face-up on the field when the Spell Card is activated and when it resolves in order to get a Spell Counter.
- Q: Is "Magical Marionette" considered to be a Multi-Trigger effect? A: No, it must be used during your MP only.
- Q: If "Magical Marionette" has 6 counters on it (which is a boost of 1200, bringing its ATK to 3200) and in your MP 1, you remove 2 of the spell counters to destroy a monster, does this card's ATK then drop 400 points to 2800? A: The number of Spell Counters on "Magical Marionette" are constantly being checked. The ATK boost is based on how many Spell Counters you have on Magical Marionette." In your example, yes, Magical Marionette’s" ATK will drop by 400, since 2 Spell Counters are being removed.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Goat forum — sourced change requests get reviewed.