When attacking with Arabella, Abandoned Doll, her ability is auto-ordered on the stack to resolve first. This makes players miss the benefits from synergies like Mobilize or Anim Pakal's "Create tokens" because those tokens enter after Arabella's trigger has already resolved.

Lowering priority might conflict with cards that add power on attack, pushing low-powered creatures above her effect before it resolves, so it seems like her effect should resolve before those, but after effects that add creatures/tokens to the battlefield upon attack.

Screenshots show the default stack order putting Arabella first, and the optimal order putting her last after all of the mobilize/create 1/1 token triggers.