Dark Dabbling is still on the stack while you count the number of instant and/or sorcery cards in your graveyard. It doesn’t count itself.
Dark Dabbling
If the target creature is an illegal target by the time Dark Dabbling tries to resolve, the ability doesn’t resolve. You don’t draw a card and no creatures are regenerated.
Dark Dabbling’s spell mastery ability is a normal spell effect, not a replacement effect. This means that if you replace drawing a card for Dark Dabbling’s effect with dredging a card from your graveyard, the cards put into your graveyard this way may enable the additional regeneration.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Bastien L. Deharme
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
