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Shapechange allows you retain your Intelligence & class features, while taking up your new forms' physical stats. In theory, this means that a Bladesinger could change into a Marilith and get 7 attacks with crazy modifiers using Bladesong, while having really high AC and Concentration saves.

However, a few questions came up:

  1. Swords Not Included™: You would need to supply 6 melee weapons rapiers to benefit get the most out of Song of Victory. How could you effectively carry these before Shapechanging, and efficiently wield them afterwards?
  2. Assuming this goes smoothly, would your weapon attacks be at +11 to hit (+5 Dex due to finesse + 6 proficiency), the Marilith's +9 (which appears to be +4 from Str, due to longswords not having finesse, and +5 prof), or +10 (+5 from Dex/finesse and +5 from proficiency)?
  3. Would the damage be 6d8 + 60 for the sword attacks (w/ Song of Victory), plus 2d4 + 9 for the tail?
  4. Would AC be 18 + 5 (Bladesong) = 23 (+5 optionally with Shield) ; and +15 Concentration Saves?

Granted, it's no Wish, but vs a handful of powerful targets (especially with Spellcasting), I feel like it could really bring enemies down quickly and hold the line, ideally if Hasted by a party member.

Khashir
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    note that the action gained from Haste can't be used for making more than one attack. It's still beneficial, but (unlike a Fighter's Action Surge) it won't double your attacks. – PixelMaster May 13 '20 at 22:58
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    Heh, wouldn't that be something? "I use my actions to attack the BBEG for 12d8+120 damage." – Khashir May 13 '20 at 23:06

1 Answers1

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Monster’s actions are not the same as PC’s actions

  1. To get the 7 attacks you need to take the Marlith’s Multiattack action - this is not the Attack action1. In particular it requires “six [attacks] with its longswords” - not your rapiers. Of course, you can use Bladesong with longswords. So, total damage would be 12d8 + 2d10 + 63.

  2. You use the Marlith’s proficiency as proficiency is not a class feature. You use the Marlith’s strength with longswords, So +9.

  3. The longswords are 2d8 + 4 + INT mod, the tail is 2d10 + 4 + INT mod.

  4. Looks right to me.

Haste would give you one extra attack - the tail is usually better.

1This is detailed on page 10 of the Monster Manual (my emphasis):

ACTIONS

When a monster takes its action, it can choose from the options in the Actions section of its stat block or use one of the actions available to all creatures, such as the Dash or Hide action, as described in the Player's Handbook.

MELEE AND RANGED ATTACKS

The most common actions that a monster will take in combat are melee and ranged attacks.

...

MULTIATTACK

A creature that can make multiple attacks on its turn has the Multiattack ability.

Now, a Marlith's Longsword action is different from the Attack action. It can choose to take the Attack action with a longsword but, if it did, it would do 1d8+4 damage (or 1d10+4 if used 2 handed) as is normal for a longsword, not 2d8+4 which is the effect of the Longsword action. Similarly, a Multiattack is not the same as the Attack action with Extra Attack such as a PC fighter might have. Multiattack has to use the specific combination specified.

Khashir
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Dale M
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    Point 1 seems like a very strict reading of the stat block—do you have any evidence/precedent to support that interpretation? Naturally the multiattack refers to its longswords: it's the correct way to articulate that idea in English. But surely a 6-armed combatant can attack six times with one blade just as well as another (regardless of who owns the weapons). – Khashir May 13 '20 at 23:56
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    @Khashir while that ruling is sensible, it is not how the rules work in practice. Multiattack only works with the specific attacks listed. Of course, if your DM and table is comfortable with adjusting the marilith stat block to allow for rapier attacks, then that is probably not particularly unbalanced (although I can't say for sure). – David Coffron May 14 '20 at 13:29
  • Ah, I hadn't caught that. Wow, it's even crazier then; who wants a rapier when you have a 2d8 longsword? – Khashir May 14 '20 at 21:29
  • @Khashir Surely it could also have used the more ambiguous word "weapons" and be just as natural. – Joel Harmon May 15 '20 at 00:38
  • In terms of carrying and wielding these, what do the rules say? I.e., this part of the question "How could you effectively carry these before Shapechanging, and efficiently wield them afterwards?" – Khashir May 15 '20 at 15:39