[RPG] Is Alter Self strictly better than Disguise Self as at-will invocations

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PHB Page 211, Alter Self

You assume a different form. When you cast the spell, choose one of the following options, the effects of which last for the duration of the spell. While the spell lasts, you can end one option as an action to gain the benefits of a different one.

Change Appearance. You transform your appearance. You decide what you look like, including your height, weight, facial features, sound of your voice, hair length, coloration, and distinguishing characteristics, if any. You can make yourself appear as a member of another race, though none of your statistics change. You also can’t appear as a creature of a different size than you, and your basic shape stays the same; if you're bipedal, you can’t use this spell to become quadrupedal, for instance. At any time for the duration of the spell, you can use your action to change your appearance in this way again.

PHB Page 233, Disguise Self

You make yourself—including your clothing, armor, weapons, and other belongings on your person—look different until the spell ends or until you use your action to dismiss it. You can seem 1 foot shorter or taller and can appear thin, fat, or in between. You can’t change your body type, so you must adopt a form that has the same basic arrangement of limbs. Otherwise, the extent of the illusion is up to you.

The changes wrought by this spell fail to hold up to physical inspection. For example, if you use this spell to add a hat to your outfit, objects pass through the hat, and anyone who touches it would feel nothing or would feel your head and hair. If you use this spell to appear thinner than you are, the hand of someone who reaches out to touch you would bump into you while it was seemingly still in mid-air.

To discern that you are disguised, a creature can use its action to inspect your appearance and must succeed on an Intelligence (Investigation) check against your spell save DC.

Can the 2nd-level Alter Self spell make the 1st-level Disguise Self spell obsolete, either by perfectly replicating the spell's effects or by providing wholly superior effects? Based on past editions of D&D I would guess yes, but after reading the descriptions of the spells from the PHB I can't quite tell.

Specifically, I'm asking this question because the Warlock gets two different invocations: one that allows at-will usage of Disguise Self (Mask of Many Faces), and one that allows at-will usage of Alter Self (Master of Myriad Forms). The Warlock can also trade old obsolete invocations for different ones during a level-up. Is it advantageous to trade the Disguise Self invocation for the Alter Self invocation? Is it optimal for a character specializing in Stealth/Disguise/Social abilities to have both?

Best Answer

Strictly better? No.

One of the major points of Disguise Self is that it can not only alter your appearance (via illusion), but your clothing and equipment as well.

It's important to note the inverse of this: Alter Self does not specify that it modifies your clothing or equipment. This means that, depending on how severe your alterations are, you may no longer fit into your armor and your clothing may clearly no longer fit you, depending on how simulationist your DM is on the topic. This is especially important if using the "Variant: Equipment Sizes" rule on PHB p.144:

In most campaigns, you can use or wear any equipment that you find on your adventures, within the bounds of common sense. For example, a burly half-orc won’t fit in a halfling’s leather armor, and a gnome would be swallowed up in a cloud giant’s elegant robe.

The DM can impose more realism. For example, a suit of plate armor made for one human might not fit another one without significant alterations, and a guard’s uniform might be visibly ill-fitting when an adventurer tries to wear it as a disguise.

Using this variant, when adventurers find armor, clothing, and similar items that are made to be worn, they might need to visit an armorsmith, tailor, leatherworker, or similar expert to make the item wearable. The cost for such work varies from 10 to 40 percent of the market price of the item. The DM can either roll 1d4 × 10 or determine the increase in cost based on the extent of the alterations required.

Even if your equipment does fit you after the effects of the spell, any well known gear or accessories may still let you be identified, especially if they're more well known then your actual physical attributes.

There are a few other considerations as well.

One of them is that both Alter Self and Disguise Self can be used at the same time, to enhance the illusion with actual physical changes underneath it. Do note that this is only possible because Disguise Self does not require concentration, which is another point in its favor over Alter Self, which does. This means Alter Self can fail earlier than intended (especially in combat or while under stress), while Disguise Self will last the duration under most conditions, and still allows you to cast other concentration spells.

Another is comparing how Disguise Self and Alter Self interact with height & size.

Alter Self actually changes your height, while Disguise Self only creates the illusion of a height change, keeping you your usual size. This might matter if your DM actually cares about character height in certain situations rather than just your size.

In addition, Alter Self restricts you to only changing your appearance to a creature of the same size with no other restriction on maximum height gain/loss, while Disguise Self only has a restriction on height change rather than size change.

For example, with Alter Self, you could change the shortest possible dwarf into the tallest possible goliath, whereas with Disguise Self, you could make a dwarf appear to be a halfling (so long as you're not trying to change your height by more than a foot in doing so).

Overall, I'd probably rate Alter Self better than Disguise Self in some combination of the following situations:

  • There is plenty of time to make preparations in advance, including having an appropriate alternate outfit ready.
  • You are unprepared, but you only need minor superficial changes with no drastic change such as size, making the lack of alternate costume not an issue.
  • You are in no danger of having your concentration broken for the next hour, nor are you likely to need to cast any other Concentration spells.
  • You are likely to be thoroughly inspected for some reason or another.

In other situations, there is a chance Disguise Self may be the more appropriate spell. In a situation requiring an emergency drastic appearance change (clothes, size, and all), for example, I would much prefer Disguise Self as my option.

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