D&D 5E What is the difference between D&D 5e and the SRD 5.1?

[Voadam]

Interesting. I always thought that slaad were declared PI like illithids and displacer beasts, but after a bit of searching that does not appear to be the case. Although I did find an FAQ that claimed it was!

I thought they were PI in the 3.5 SRD but I just checked and nope.

Funny enough Slaadi are not PI in the 5.1 SRD and are referenced in the monster types as quintessential aberrations alongside aboleth, beholders, and mind flayers (beholders and mind flayers being kept closed by the PI designation in the document).

Immediately after the SRD 5.1 PI designation it says "All of the rest of the SRD5 is Open Game Content as described in Section 1(d) of the License."

 

[Ariel23]

There's a general list of changes and some other explanations at Wizards:

Systems Reference Document (SRD) | Dungeons & Dragons