Edit: With 5.2.1 the Octopus was added to the SRD. Issue resolved.
In the players handbooks, in appendix b, are stat blocks for creatures used by players. There was an errata:
"All Stat Blocks (pp. 346–359). All stat blocks in appendix B have been replaced with the Monster Manual (2025) versions."
All of the creatures in this appendix are in the SRD 5.2 except 2: Octopus, Slaad Tadpole
It looks like Octopus was left out by mistake. It is mentioned in the Find Familiar spell in SRD 5.2. But there is no stat block for it.
"You gain the service of a familiar, a spirit that takes an animal form you choose: Bat, Cat, Frog, Hawk, Lizard, Octopus, Owl, Rat, Raven, Spider, Weasel"
There is a stat block for Giant Octopus. Octopus is also in the SRD 5.1 for the 2014 rules.
I think Slaad Tadpole could also be added to the SRD if you renamed it.
Edit: With 5.2.1 the Octopus was added to the SRD. Issue resolved.
In the players handbooks, in appendix b, are stat blocks for creatures used by players. There was an errata:
"All Stat Blocks (pp. 346–359). All stat blocks in appendix B have been replaced with the Monster Manual (2025) versions."
All of the creatures in this appendix are in the SRD 5.2 except 2: Octopus, Slaad Tadpole
It looks like Octopus was left out by mistake. It is mentioned in the Find Familiar spell in SRD 5.2. But there is no stat block for it.
"You gain the service of a familiar, a spirit that takes an animal form you choose: Bat, Cat, Frog, Hawk, Lizard, Octopus, Owl, Rat, Raven, Spider, Weasel"
There is a stat block for Giant Octopus. Octopus is also in the SRD 5.1 for the 2014 rules.
I think Slaad Tadpole could also be added to the SRD if you renamed it.