Quote Originally Posted by RSP View Post
The spell doesn’t target the caster though. It affects those who are hit with it.

Just so we see if we’re on the same page, here’s my view on similar issues with DM:

1. Casting DM on a creature Concentrating on Haste cast on a different creature does nothing to the Haste: you can’t “dispel” the Concentration.

2. If Sally casts Magic Weapon on Steve’s sword, BBEG casting DM on Steve doesn’t effect the MW spell, as it’s on the weapon, not Steve.

3. If a Wizard casts Creation to make a diamond, and holds that diamond in his hand, while BBEG casts DM on the Wizard, the diamond will not be affect by the DM.

Just want to see if my basic understanding of DM matches with others.
The spell does target the caster though, that is what range self means. If Dispel Magic is targeted at the caster, it will dispel Sahdow Blade, there is no ambiguity for me there. Now you could argue if it targeted the blade, the blade would wink out, but the caster could theoretically re-summon it with a Bonus Action. That depends on whether you think Dispel Magic should work on every aspect of a spell or just the pieces it's targeted at (most conjuration spells are going to depend on this question). I am not sure how I feel for example that dispelling a single animal in Conjure Animals removes the rest and ends the entire spell.

As for your bullets:
1. This is the most questionable to me. If a spell requires concentration, there is clearly some link back to the caster as they have spend ongoing effort to keep it going. So does Dispel Magic break that link and end the spell? I am not sure, I could go either way depending on the logic of magic in the world. By RAW/RAG I think you're right, but I can be convinced otherwise.

2. This is right. But see question 1 if the spell targeted Sally.

3. I agree here.

Quote Originally Posted by RSP View Post
This is just incorrect, per the RAW of DM:

“Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends.”

You chose the creature, and the spell ends on that target, not in general. So if 8 rabbits are summoned, casting DM on one of them would only dispel that one.
This may be technically correct, but there is room to make a different determination depending on the logic of magic in the game. It also will depend on the concentration ruling if the caster of Conjure Animals is targeted.