paper quiver
It would be an evolution that needs poisonous saliva to be used, and when you upgrade poisonous saliva to max you get a branching evolution that changes your poison ticks into one of two types of venom. The top evolution would be called Hemotoxin and it turns any and all poison ticks into bleeding ticks that do more damage the lower health an enemy is, also when enemies are inflicted with Hemotoxin I think it would be cool to see red discoloration around the eyes/mouth of the enemies. The bottom evolution would be Myotoxin that slows and progressively paralyzes enemies inflicted with the poison ticks.
(Hemotoxin inspired by Boomslangs and Myotoxins inspired by Inland Taipan.)
Physical appearance: For the Boomslang specifically, make darwin turn green with black stripes on his belly. For the inland taipan, make Darwin black and have a yellow belly. Both should get longer fangs, maybe with a drip/saliva effect with the different toxins. (bright yellow--Myotoxin/purple--base toxin/amber-Hemotoxin.)
sly peak
lusty locust