Is the homebrew weapon attack cantrip 'Arcane Strike' balanced?

Question

I have created some new cantrips which include making a weapon attack as there are only two official ones to choose from. I've tried to follow these principles based on Booming Blade and Green-Flame Blade:

• Melee weapon attack only, 5 foot range
• No unavoidable extra damage to the primary target at level 1
• Damage no more than 2 targets
• Spellcasting ability modifier doesn't have to affect the spell at all
• Only available on the Warlock, Sorcerer and Wizard spell lists

But with such a small amount of official content to compare them against, it's hard to say if they're balanced.

Is this spell balanced with Booming Blade and Green-Flame Blade?

Arcane Strike

Evocation cantrip

Casting Time: 1 action
Range: 5 feet
Components: V, M (a weapon)
Duration: Instantaneous

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails.

On a hit, the target suffers the attack's normal effects, except all bludgeoning, piercing and slashing damage from the attack is converted to force damage.

At 5th level, the attack deals an extra 1d6 force damage to the target. The damage roll increases by 1d6 at 11th level and 17th level.

Answer 1

Almost certainly balanced, possibly underpowered

It seems that the intent is to give a melee caster some damage that can affect creatures resistant or immune to non-magical weapons (or the fire and thunder types of the other "blade" cantrips). In that case, you could simply make the effect "the weapon is considered magical". Force damage, while being the least resisted, is still more resisted than straight up magical weapon damage, I believe.

So, we have a couple points of comparison. The second level Magic Weapon, which also gives the weapon a +1 to hit and damage, and lasts much longer, and can be used on an ally's weapon.

The Druid cantrip Shillelagh, which has a longer duration, potentially increases the damage to a d8, but still requires using the spellcasting ability modifier to attack and is limited to clubs and staves. It also takes a bonus action to cast, which lowers the action economy for the first round (taking a bonus action and an action to attack), but then maintains better action economy subsequently, since it allows multiple attacks per round via extra attack and two-weapon fighting. It does not scale the damage as the caster levels, making it less useful (and possibly useless) after the caster gets a magic weapon (a d6 damage weapon with +1 to damage being effectively equivalent to a d8 weapon with no bonus as Shillelagh provides).

So, for the most part, it is superior to Shillelagh, inferior to Magic Weapon (as it should be, though since it would stack, you could use both), and quite possibly inferior to Green-Flame and Booming Blade in most situations, since at high levels the user should have a magic weapon and thus not suffer from an opponent's resistances, and at low levels very few opponents would have those resistances. There are, of course other possible comparisons, but I think these are sufficient to determine the spell's appropriateness.

In short, I feel that it is niche enough that it is probably under powered, but since its damage scales, it could certainly continue to see use even after the caster has a magic weapon, especially since the bonus damage type will be resisted much less than that of GFB and BB.

In fact, that might make the best comparison of all - you lose some conditional damage and use a smaller die for the bonus damage in order to get a better damage type. One or the other of those might be sufficient to make it balanced, but with both it is certainly in little danger of being overpowered.

Answer 2

The Spell is fine, maybe somewhat underpowered

Consider the comparison to Booming Blade: Arcane Strike gains the advantage of dealing a damage type that very few creatures have resistance (or vulnerability!) to, but its direct damage is lower, and without the secondary effect of Booming Blade, it also lacks the combat-control features.

If you bumped the extra damage up to 1d8 instead of 1d6, you'd probably be right on par with what you'd expect from a spell like this: It doesn't meaningfully deal more damage than what you'd expect from Booming Blade, but does function as a "if all else fails" option for dealing with creatures that have difficult resistances.

Answer 3

Not balanced

Shifting the entire weapon attacks damage type from something some creatures are resistant to something most aren't is a huge deal. Adding the 1d6 (scaling) extra damage just pushes this overboard.

It's smaller than the 1d8 of BB or GFB, but that's I think negligible compared to changing the damage type of your entire attack.