So I've been playing D&D 5th edition with a few guys and I'm going to roll a new character, which they are all in favor of. I've taken a liking to an archer, but more specifically an archer with arcane routes.
This has lead me to discover the "Bladelock" or, officially, the Warlock with the Pact of the Blade feature. Additionally, with the Unearthed Arcana's release of new Warlock subclasses and features (found here) there is an invocation called the "Moonbow".
The Moonbow is the Warlock's only means of having a ranged pact weapon, and it's pretty neat. It has advantage on attack rolls against lycanthropes - meh. It can also merge with a magic bow you may possess, but it's main draw is its Holy Smite-esque feature; it allows you to expend a spell slot that can add 2d8 worth of extra damage per spell slot level.
This is my dilemma. While I know you can use other class' spell slots to fuel this ability, say a Sorcerer's 9th level spell slot, I can't determine if it is specifying that you can only use "one" spell slot at a time, or if you can stack multiple spell slots together.
You can create a longbow using your Pact of the Blade feature. When you draw back its string and fire, it creates an arrow of white wood, which vanishes after 1 minute. You have advantage on attack rolls against lycanthropes with the bow. When you hit a creature with it, you can expend a spell slot to deal an additional 2d8 radiant damage to the target per spell level.
If it is specifying only one spell slot at a time, does that mean one per hit (multiattack features), or merely once per turn?
If anyone had any ideas or interpretations on this, please let me know. Thank you!