Are these homebrew metallic/chromatic pseudodragons the same CR as RAW pseudodragons?

Question

Pseudodragons are Tiny CR 1/4 dragons, but they're not quite dragon-like enough for my purposes. I want to homebrew some alternative stat blocks to the pseudodragon so that they more so resemble the various metallic/chromatic dragons, but at the same time I'd prefer it if my changes didn't change their overall CR. Specifically, I want to add damage resistance and a breath weapon, similar to "true dragons", resulting in 10 variations of the pseudodragon, and I want these 10 variations to still all be CR 1/4.

To that end, I have swapped out their Magic Resistance trait for the damage resistance that relates to their colour (as per the Draconic Ancestry table of the dragonborn playable race, for example) and have swapped out their Sting attack for a Breath Weapon attack (again, taken directly from the dragonborn playable race, assuming the lowest possible number of damage dice; i.e. 2d6 from a level 1 dragonborn PC). I'd have the DC for the breath weapon be the same as the DC for the Sting attack, and I'd have it on a Recharge 6, same as, say, a dust mephit's Blinding Breath.

If I were to make these changes to the pseudodragon, would it still be the same CR? Is this true for each "colour" pseudodragon (i.e. does fire damage vs. cold damage make one variant inherently more powerful than the other, etc)? I'm hoping that they're all the same CR (ideally CR 1/4), regardless of the damage type resisted/dealt via breath weapon...

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If this isn't too much for one question, assuming that they are all balanced against each other regardless of damage type, as I hope, then if I were to add a 15 ft. swim speed and the Amphibious trait of certain dragons that can swim and breathe underwater (such as gold dragons) to the corresponding pseudodragons (i.e. my gold pseudodragon), would that make much of a difference to their CR vs. those that would not have those traits (i.e. my red pseudodragon)?

I'd probably also want to add a 15 ft. climb speed to the pseudodragons that are of the same colour as true dragons that have climb speeds, i.e. my red pseudodragon (although given that pseudodragons can fly, I'm guessing this is of no consequence to the CR, but I thought I'd mention it just in case it matters).

Answer 1

Their calculated CR remains the same, but they are far stronger

Carcer rightly points out the way your CR is calculated, but I feel like that doesn't capture the entire picture.

I feel like this pseudodragon may very well be punching above its 1/4 weight with a 2d6 breath weapon. With a lucky roll, there's a good chance it could knock out an entire first level party in a single breath weapon. CR 1/4 indicates it should be roughly 2-3 pseudodragons to form a decent challenge for a first level party, but 2-3 pseudodragons with this breath weapon will absolutely annihilate any first level party round one if they know how to aim.

Ogres suffer from a similar problem. If you calculate their CR, it comes down to a CR 1 creature, but they are still listed as a CR 2 creature, simply because there's a really good chance that it'll oneshot a first level character.

On top of that, you've replaced their attack which requires getting in melee range with a breath attack they can use from a distance. This, combined with a fly speed of 60, means they can very easily fly into range, breath weapon, fly away, and then fly away until their breath weapon has recovered, before coming again for a new run.

This is at a level where most characters will have very few ways of dealing with a flying opponent.

I for one would not want to face even one of these creatures at level 1.

If the breath weapon is changed to be once per short rest instead of Recharge 6, it'll at least make it a lot more manageable because it can't hit and run. Also reducing the damage to 1d6 may very well be enough to keep it around roughly the same challenge rating. It'll at least no longer be something I'd really dread fighting at level 1.

As an aside, regarding being used as a familiar (say, for a Warlock via Pact of the Chain), it's most likely not that big a deal, I doubt it'll be more impressive than invisible scouts. Familiars used for combat purposes tend to be dead familiars before long. It'll be good for killing some goblins every now and then, but it'll be costly to keep resummoning your dead familiar.

Answer 2

Roughly, yes, their CR should be the same

Applying the DMG's guidance on modifying monsters and calculating challenge ratings, I reckon your modified pseudodragons are roughly on par with standard pseudodragons. Specifically:

Defensive CR

The pseudodragon's normal Magic Resistance trait is much more useful than damage resistance to one elemental damage type. The DMG suggests MR is comparable to raising a monster's AC by 2 for defensive CR purposes, but resistance to a single damage type has no effect on a monster's CR - it's too easy to bypass and will be rarely relevant.

A standard pseudodragon has a defensive CR of 1/4 only because of its Magic Resistance. Without that benefit, the estimated defensive CR drops to 1/8 (for a creature with 7hp and an AC of 13).

Offensive CR

Replacing the pseudodragon's sting with a 2d6 AoE breath weapon increases their potential damage output. Averaging over three rounds of combat as the DMG describes, having the breath weapon raises its DPR from 4.5 to 8.33 (assuming it uses the breath weapon once and affects two targets).

That would bump the pseudodragon's offensive CR from 1/4 to 1/2 (as it averages ~8 DPR and its attack bonus is within two points of expected for CR 1/2). The possibility of being poisoned by the normal pseudodragon's sting isn't something the DMG's guidance actually takes into account, since it doesn't describe how to adjust CR for such attack riders (indeed, the chance to impose a condition on targets is described as a "flavorful twist"...) so I've not worried about it.

Final CR

Altogether, your modifications drop the creature's defensive CR by one step but raise its offensive CR by one step, so that still averages out at CR 1/4. Extra details such as adding the (mostly redundant) climbing speed, Keen Senses, etc. are irrelevant for determining CR since they would have no material impact on the creature's combat efficacy.

Practically, I would actually expect your modified pseudodragons to be somewhat more effective in combat than default pseudodragons are, purely because they can open by using their breath weapon and do more damage in one round than a default pseudodragon could hope to. At a mere 7hp/AC13, pseudodragons were already extremely unlikely to survive more than one round in combat, so this improved first round burst damage gives them an edge over their default cousins. For this same reason, I don't think it matters what you set the breath weapon's recharge to - the pseudodragon is extremely unlikely to get to use it more than once.