Contagion Spell Odds

Contagion is a 5th-level necromancy spell that requires an attack roll and a “best of 5” save mechanic before inflicting a disease (Player’s Handbook p. 227). Is this a good spell? Let’s look at the mechanic to see how often its successful.

Contagion Mechanics

First, you must make successful a melee spell attack. The range of this spell is touch, so you typically have to be within 5 feet of your creature, although this can be extended to 100 feet with the Find Familiar spell.

When you hit the target, the spell has no effect, but causes the target to make Constitution saving throws at the end of its turns. Although the spell language states that “your touch inflicts disease” and that either “the disease’s effects last for the duration” upon the third failure or “the creature recovers from the disease” upon the third save, D&D Lead Rules Designer Jeremy Crawford has ruled that the spell has no effect until the “best of 5” save mechanic is resolved:


If the target makes three Constitution saving throws before they fail three Constitution saving throws, the spell has no effect. Bummer.

Upon failing three saves, the target is subjected to your favored selection of a half-dozen diseases that each impose disadvantage on skill checks and saving throws tied to a specific ability score, plus some other goodies. Pretty nasty stuff.

Since you’re using a 5th-level spell slot and waiting at least three turns after making a successful melee attack, you probably want to know how likely it is that the Contagion will actually take effect.

Contagion CalculatorContagion 9

Here’s the chance of success for a standard character that’s just unlocked Contagion at Level 9. They’ve achieved a 20 in their primary ability score by using their first two Ability Score Improvements (ASIs) to cap it out (or by rolling stats). We can assume that the D&D designers use this guideline, since feats are optional.

If you have different stats, you can plug them in to see your own odds! Add any special DC bonuses (i.e. Robe of the Archmagi, Rod of the Pact Keeper) directly to your Spellcasting Ability Modifier.

Here’s a sampling of Constitution saves from the 5th Edition Monster Manual, to provide some context for the chart:

Con Save Samples.png

Disadvantage on Saves

What if the target of Contagion has disadvantage on its saving throw? This is tough to wrap in one package, but possible for Clerics and Oathbreaker Paladins.

Contagion is available to Clerics and Druids. Warlocks originally didn’t get Contagion, but patrons of The Undying do via their expanded spell list (Sword Coast Adventurer’s Guide p. 139). Contagion is also accessible to the Oathbreaker (Dungeon Master’s Guide p. 97), a villainous Paladin class option. Contagion most recently appeared in the January 2018 Unearthed Arcana, where it was on the Circle of Spores Druid’s expanded spell list (which does not expand the list of classes that can cast it).

Bestow Curse. Bards, Clerics, Wizards, Oath of Conquest Paladins, and Oathbreaker Paladins get access to Bestow Curse. After the target fails a Wisdom saving throw, you can impose disadvantage on their ability checks and saving throws with the selected ability score. When cast at 5th level or higher, this spell does not require concentration. The obvious downside here is that you’re introducing yet another saving throw, and potentially delaying the efficacy of Contagion by yet another turn.

Portent is the a Divination school ability that allows Wizards to substitute a target’s saving throw for one of their saved portent dice. This effectively functions as “super disadvantage” because the player has access to two additional dice. However, Wizards don’t have Contagion on their spell list.

The options for combining these effects are limited. Recognizing that a party often works together, including focus-firing on a BBEG, it’s still worth giving the save disadvantage numbers a look. The checkbox on the calculator will show your Contagion’s chances against a target with disadvantage on Constitution saving throws.

You can see this gives a significant bump to the +5 Spellcaster at Level 9:

Contagion 9D

Here’s a comparison at the Level 13 to 16 range:

Here is the comparison at the Level 17 to 20 range:

Keep in mind, these are all after you’ve landed a successful melee spell attack. So…

Should Contagion Inflict Disease-On-Hit?

Contagion is the only spell which requires an attack followed by the “best of 5” save mechanic. For a 5th-level all-or-nothing spell, you should be getting something thats better than banishing a creature to another plane of existence. An easier fix is conforming Contagion to common spell design–a temporary benefit unless a saving throw is made.

Attack+Save Spells

Typically, spells which require a saving throw do not require a spell attack, and vice versa. There are only two other types of spells which require a successful attack and a failed save to have any effect:

  • Ranger Arrow Enhancer Spell
    • Ensnaring Strike (1)
  • Banishment Spells
    • Dispel Evil and Good: Dismissal (5)
    • Plane Shift (7)

Many spells add a little extra damage with a save for a secondary effect, but aren’t left naked if they fail. Spells that don’t get that automatic damage/effect have to do something good to make up for it.

Ensnaring Strike. Restrained is a very strong condition to impose, especially when it causes recurring damage until escape. This spell is also relatively inexpensive, only costing a Bonus Action to cast at a Level 1 slot to cast.

Dispel Evil and Plane Shift. When you ramp up the spell level while keeping the attack+save requirement, the result is the power to eliminate the threat entirely. In the case of Dispel Evil (a 5th-level spell like Contagion), you gain protection until you end the spell by triggering the dismissal effect. Plane Shift also has a lot of utility beyond the banishing effect, allowing you to traverse the planes with your entire party.

If you feel that the effects of Contagion are similar to banishment, feel free to allow it to inflict disease when the melee spell attack hits. A temporary advantage until a save is more in congruence with how other spells were built in 5th Edition.

Concerns with Disease-On-Hit?

Slimy Doom. One concern with allowing Contagion to automatically apply is that picking the Slimy Doom disease will cause the target to become more susceptible to permanency (7 days). This is because Slimy Doom causes disadvantage to Constitution saving throws. You can see the effects of this by checking the check box on the calculator. Any other disease will not affect the odds of saving against the spell.

Suggested Fixes. Trade a nerf for immediate effect:

  1. Remove disadvantage to Constitution saving throws. The fact that Slimy Doom allows you to stun-lock the opponent is already powerful enough. Removing the draw of the self-fulfilling choice will make the spell more diverse, as the other options become more attractive.
  2. Contagion doesn’t effect the saves it causes to be made. This can be a good option if you feel that the above is too strong or you’re comfortable being a little more fiddly.
  3. Temper the effects until the saves are failed. This allows Contagion to be treated like other spells. For example, Flesh to Stone will restrain the target on the first failed save, but they will only turn to stone after failing a “best of 5” save test. In the case on Contagion, consider allowing the player to pick one new disease effect for each failed saving throw.

Unless your DM is willing to concede to one of the suggested fixes above, Contagion comes out relatively underpowered for a 5th-level spell, due to the likelihood that it just won’t do anything in combat. Contagion can still serve as a fun narrative spell, with its 7 day duration, though its verbal and somatic components betray the typical poisoner’s style.

Now, go forth and spread disease!

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