How to design D&D 3rd ed Rogue's Sneak Attack in M&M3e?

Question

How to design D&D 3rd ed. Rogue's Sneak Attack in M&M3e? What effects are being utilized?

My first idea was a Affliction X vs Dodge or Parry, for an additional degree of failure to a Toughness resistance save, Linked to Damage Rank X; that or a way to reduce Toughness quicker.

Answer 1

It varies with Descriptors

Sneak Attack says:

If a rogue can catch an opponent when he is unable to defend himself effectively from her attack, she can strike a vital spot for extra damage.

The rogue’s attack deals extra damage any time her target would be denied a Dexterity bonus to AC (whether the target actually has a Dexterity bonus or not), or when the rogue flanks her target. This extra damage is 1d6 at 1st level, and it increases by 1d6 every two rogue levels thereafter. Should the rogue score a critical hit with a sneak attack, this extra damage is not multiplied.

Ranged attacks can count as sneak attacks only if the target is within 30 feet.

With a sap (blackjack) or an unarmed strike, a rogue can make a sneak attack that deals nonlethal damage instead of lethal damage. She cannot use a weapon that deals lethal damage to deal nonlethal damage in a sneak attack, not even with the usual -4 penalty.

A rogue can sneak attack only living creatures with discernible anatomies—undead, constructs, oozes, plants, and incorporeal creatures lack vital areas to attack. Any creature that is immune to critical hits is not vulnerable to sneak attacks. The rogue must be able to see the target well enough to pick out a vital spot and must be able to reach such a spot. A rogue cannot sneak attack while striking a creature with concealment or striking the limbs of a creature whose vitals are beyond reach.

This is equivalent to getting to deal additional damage to Vulnerable or Defenseless targets. Flanking isn't a thing in M&M3, so I'm going to ignore that part.

The description can also be an explanation for why the target doesn't get to use Defensive Roll advantages against the attack. Again, this only applies to Vulnerable or Defenseless targets.

Note that any successfully rolled attack against a Defenseless target is automatically a critical hit (see Basic Conditions, Hero's Handbook page 17).

So, a designer has a few options for introducing "Sneak Attack" into M&M3.

1. The easiest is a description on attacks against Vulnerable targets - many of whom rely upon Defensive Roll advantages to increase Toughness beyond mortal limits.
2. The most satisfying is Ranged Damage X, Limited (Vulnerable or Defenseless targets) for 1 point per rank. This is subject to PL caps, so attack bonuses may drop. You can add a Quirk to only affect targets with Stamina (flat -1) to keep that restriction and make the first rank basically free.
3. Next is a combination of advantages, notably Power Attack, used when attacking Vulnerable targets. This doesn't feel special in play, making it a poor choice.

There are other combinations that may work, but those are the closest to SRD sneak attack.

Answer 2

3E has various situational Advantages which give you a bonus in certain situations such as Favored Environment, which gives a +2 to either Attack or Defense when in your preferred environment (+5 with the second rank).

It seems reasonable to me to allow either a +2 (for one rank) or a +5 (for two) for a Sneak Attack advantage that works against Vulnerable or Defenseless foes. A GM would be well-served to check to be sure that the player's build isn't such that this applies all of the time instead of occasionally or situationally.

Answer 3

For a melee character, Enhanced Attribute: Str (Limited to Damage, Limited to Vulnerable Targets) comes out to +2 to damage for 1 PP spent to purchase the power. Ranged Attacks would be built similarly, with either Enhanced Trait: Throwing Mastery (Limited to Vulnerable Targets) for 2 damage per PP or Blast (Limited to Vulnerable Targets) on some ranks of your Blast for twice as much.