These are great suggestions and I’ll dig more into them after the update, however:
Arachna’s won’t need the Agility updates. They have (as of the v.9 update) a race-specific Mass Web ability. It is similar to a weaker Debilitate with a longer cool down, but should add some fun racial quirks to fights. I needed a distraction from the farm upgrade one night and played with it.
I like the idea of a poison for Lamias. Eventually any race (or person, if added via laboratory) with wings will have the Fly ability. Beyond that, if you think of any others that could be appropriate to various races (vaguely based on existing abilities just for simplicity and sanity), chime in!