Troll with snake eyes. Thoughts on abilities this might give them? Snake eyes would look like this probably (sorry for the trouble btw)
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I wouldn’t see any real problem with such a mutation, I've seen plenty of Trolls with various degrees of snake-like eyes, be them round with simple points above and below, or outright vertical lines.
In the cases I've seen the shape of the pupils was nothing more then a mere shape, not really granting any unusual abilities or visions. If you’re looking for suggestions however, heat-vision could be a possible thing as it’s theorized that some snakes are capable of seeing in infared, allowing them to see prey as glowing balls of colour on a darker background.
Being limited to only the one colour may be a limitation however as the Troll would have trouble identifying the various castes as a result. My personal suggestions in this would be to have one of the following traits occur if you decide to go with the heat vision idea.
A. the heat vision applies to only one eye, and the other (possibly looking normal) sees the usual spectrum of colour.
B. The Troll has the ability to turn the vision on and off such as Vriska’s vision eightfold.
or C. no special vision and just has snake eyes for the sake of being neat.
if you do decide to go with some sort of vision ability, altering the eye slightly to differentiate it from non-vision snake eyes may be ideal. Such possibilities could include a hard but transparent skin permanently covering the eye(s) (making them not need to blink), having squiggly patterns around the eye, or giving the typically yellow portion of the eye a different colour such as a more golden brown or even red. This would help differentiate the vision eyes from Trolls who just have snake-like eyes with no special qualities.
i hope this helped and gave you some ideas on what to do with your Troll. If possible, i highly recommend researching snakes a little more to see if there are any viable alternatives to the heat-vision thing. I hope this has helped!