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?

Viper Strike

Conjuration 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, and it must make a Constitution saving throw or take 1d8 poison damage.

At 5th level, the melee attack deals an extra 1d8 poison damage to the target, and the damage the target takes if it fails its saving throw increases to 2d8. Both damage rolls increase by 1d8 at 11th level and 17th level.

  • \$\begingroup\$ What spell list would this go on? Its utility would be very different if it were on the Eldritch Knight list opposed to the Sorcerer list, for example. \$\endgroup\$
    – GreySage
    May 10, 2019 at 18:27
  • 2
    \$\begingroup\$ @GreySage Both Booming blade and Green-flame blade are on Warlock, Sorcerer and Wizard (and therefore Eldritch Knight and Arcane Trickster) spell lists. This would be the same. (I think balancing spells like this for other classes would be impossible as there's no precedent.) \$\endgroup\$
    – Richard
    May 10, 2019 at 18:36
  • \$\begingroup\$ Something to consider for all these cantrips; cantrip damage usually only increases by 1 die/5levels, these increase by 2. While they may be balanced around low level characters, at high levels they will become much stronger (7d8+melee at level 17). \$\endgroup\$
    – GreySage
    May 10, 2019 at 18:44

2 Answers 2


Slightly OP, but pretty close.

Both BB and GFB have 'triggers' that must be passed in order to activate the extra damage (moving and another target in range). This has a similar damage addition with a similar trigger requirement (making a save.)

However, with BB, they simply choose not to move. They can't just not to make the save here. Because of that, I'd recommend dropping the damage down to D4s(scaling).

  • 4
    \$\begingroup\$ While the damage is a little high, poison is an often resisted damage type. My opinion is a D6 would make it balanced \$\endgroup\$
    – RMalke
    May 10, 2019 at 21:33

I think BB is slightly weaker than this cantrip overall, because you "choose" to suffer or not the extra damage. You can balance this by making the cantrip consume the bonus action as well or by lowering the scaling.

But if a significant part of the enemies in your campaign will have resistance to poison (like undead), you can leave it as it is.

  • 1
    \$\begingroup\$ Welcome! Usually you would want to support your reasoning by citing rules and making an effort in comparing your reading with similar situations. \$\endgroup\$
    – Akixkisu
    May 10, 2019 at 20:44
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    – V2Blast
    May 11, 2019 at 0:20

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