I find the resistances of this monster difficult to parse out.

Is it resistant to the listed energy types if the damage is from a magical effect, or is that only for the physical damage types?

The key is the punctuation, specifically the semicolon between the non-physical and physical types:

"Damage Resistances Acid, Cold, Fire, Lightning, Thunder; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks"

Put another way, Shadows have damage resistance to all Acid, Cold, Fire, Lightning, and Thunder damage. They also have damage resistance to non-magical Bludgeoning, Piercing, and Slashing damage.

I know that they are weak to radiant but how is a "SHADOW" resistant to FIRE 

How do you burn a shadow?

+10 points for House Chu

By burning whats making it

How is this challenge rating 1/2? It can literally 1-2 hit weak characters. It's going to get used though, I like it.

For 1/2 CR this is vastly OP IMO

my question is HOW IS THIS CHALLENGE RATING 1/2??!?!??!?!? It can kill high level players within a min 5-6 turns! And resistant to nonmagical weapons? i know it was meant to be a challenge but how and why are lvl 1-3 players going to have magical weapons?

This monster is way overpowered. It can literally kill a level 20 character in only two hits, or to put it another way two Shadow's can kill anything with strength 8 or lower in one round.

The ability score drain is a leftover from previous editions and should be taken out of 5th Edition by an Errata.

Or do 1/2 damage done

It has +4 to hit. Very unlikely to always hit such a high level character, especially wizards who would probably have a shield spell up their sleeve. Protection from evil spells would also make them child's play to defeat.

Quote from Gehrigan >>

It has +4 to hit. Very unlikely to always hit such a high level character, especially wizards who would probably have a shield spell up their sleeve. Protection from evil spells would also make them child's play to defeat.

 A natural 20 always hits...

It's still a CR 1/2...

I ran it last night against my party of level 1 characters, and I had to remove 1d6 from its damage, or it would have murdered them. Thankfully, the Wizard passed his metagaming check  Arcana check to realize that they were, and magic missiled them

Fun Mini-Wraith

Not in every dms mind ^^

needs to mention the Bonus to Sneak that it talks about in the MM, as well as the Undead Nature

• Skills Stealth +4 (+6 in dim light or darkness)

• Undead Nature. A shadow doesn’t require air, food, drink, or sleep.

I have access to the MM, the Entry is listed here:

• https://www.dndbeyond.com/sources/mm/monsters-s#Shadow

Comparison to this entry reveals a lack of information which should be in this entry, as this is otherwise a Different creature, and should be noted as such somewhere.

Quote from DnD_Nerd >>

By burning whats making it

It is making itself, as the Host it was previously attached to has since died. So, again, you are brought back to the question: How do you burn a Shadow? A thing which literally has almost no tangible form and by nature is never seen by a Flame in the first place until released from its Host via another Shadow's forceful interaction.

What happens to a shadow that gets hit by lightning? 

Not much... :)