One of my players has an interesting idea for combining a bard and a cleric. He'd start as a bard and become a cleric later. Can he get both the cleric's Commune and Cast a Spell with just one Multiclass Dabbler?
When you choose a starting move that depends on another starting move for your Multiclass Dabbler choice, you get both. The rules cover this (Dungeon World, Chapter 2 “Playing the Game”, § “Character Change”, p. 30):
The multiclass moves allow you to gain moves from another class. You get to choose any move of your level or lower. For the purpose of multiclassing, any starting class moves that depend on each other count as one move—the wizard's cast a spell, spellbook, and prepare spells for example.