I would perhaps suggest the
Sundew. There tentacles and glue traps make them interesting.
Other than that, Black Widows are common enough to be looked at for their venom. Larger creatures could make more, and enough of it would be deadly.
Sundews would mostly serve to be mutated for larger vines with enough mobility and strength to make them dangerous once the prey is fully ensnared, but the first unit would end up being stationary. It could later be mutated into another, or perhaps a form of symbiosis could be achieved with a giant spider, creating an active hunter.
As a plant, it is a good first option for that path, and Antdogs can likely avoid it and trick opponents into them.
It would be nice if it would also listen to certain pheromones too as something programmed in.Alternatively, Hemlock or the Castor Oil Plant mentioned earlier, and a modification for things to be produced as an areosol. Though if that resultant plant and the Sundew were to be combined, it would be a very deadly plant.
Likewise, mixing Sundew and beast to create a plantoid dog. Something with vines hanging off it capable of grasping and holding on, and enough acid to burrow in and kill that way.
Alternatively, just grab a wasp/bumblebee pattern.
Bullet Ant. Giant Japanese Hornet. Doberman Pinscher.
Bullet Ants have a painful bite. Doberman are already intelligent, strong, and good hearing, not to mention size. Giant Japanese Hornets are already large, so only need a proper venom to make them deadlier, along with a control mechanism..
Thinking, Dogs and Sundew should be easy enough, since one is a plant, the other a dog. We could do Red Ants too, which would end up giving us three easy things, but might as well do Bullet Ants for their effects. The pain will be useful, and it's not directly deadly.