Keywords are applied to types to further detail a given creature. Keywords are relevant for the purposes of other rules which specifically reference them. I am not relying on a specific set of rules, so for my purposes keywords will be relevant mainly for in-character rather than out-of-character purposes. This makes it easier to distinguish player and character knowledge rather than making a monster knowledge check because a monster's type is unintuitive.
The beast type refers to creatures of any level of intelligence which have little or no capacity for even the most basic civilization (the minimum threshold is pre-industrial indigenous cultures). Apes are considered beasts because while they have opposable thumbs, use simple tools and live in family groups, they do not have language or build shelters. Dolphins are considered beasts because they lack opposable thumbs, even though they are otherwise highly intelligent. Ravens are considered beasts because while they may be taught to speak, they lack all but the most basic kinds of tool use. Likewise for fantastical beasts, since I'm not arbitrarily distinguishing magic from nature.
From there, there are several keywords which may be used to further distinguish beasts. These keywords are based primarily on OSR.
- Animals are beasts of subhuman intelligence, usually vertebrates. This includes both animals that existed in the real world and the fantastic animals of myth and legend (which are normal parts of the fantasy ecology). Animals may be taken as animal companions and familiar rather than cohorts or henchmen where applicable. [Optional: Restricted animals are animals with abilities that may be considered game-breaking if they are allowed to be taken as animal companions, such as griffons, owlbears, cockatrices, etc.]
- Vermin are beasts of such low intelligence that they are essentially meat robots. This includes most invertebrates (cephalopods are considered animals due to their higher intelligence). In some cases they may be tamed, such as by mite fey or vermin druids.
- Blobs are beasts of vermin intelligence with amorphous bodies. This includes jellies, oozes, slimes, puddings, jellyfish, gelatinous polyhedrons, etc. Blobs may also fall under the vermin keyword.