Synx grow throughout their entire lifespan and the rate at which they do is directly proportional to how much and at what frequency they are feeding. Much like a snake, synx bodies seem rather good at evenly distributing weight. One that overeats will not simply become obese, it will actually get larger. At this point, a synx usually dies if outside of its nebula because they cannot feasibly exist as a parasite anymore. On regular planets land animals as big as elephants (or bigger) are just as rare as they are on earth, meaning the bigger a synx is, the harder the time it is going to have to find a place to decontaminate. Synx can cope with the innards of alien animals much better than an alien environment.
There are however some exceptions to this rule. Particularly resilient and lucky synx - as few as they may be - manage to survive this ordeal once they reach this age/size, then continue their existence as a predator exclusively. Over time these individual synx still grow ill, but they are strong enough to live through the initial infections, then survive with them perpetually. This is a Weeper, and while more formidable than a regular synx, these animals deal with quite a bit of ailment and misfortune for the rest of their lives. The name 'Weeper' is derived from the infections these synx accumulate: infections that cause blood to seep out from every orifice, most notably the eyes.
Weepers are usually distinguishable by elongated jaws and feet/hands appearing to have been stretched into lengthy graspers. While regular synx can have these features, this is a specific trait obtained by the physical stress of fighting and consuming large animals consistently. Weepers have also been witnessed having two tones or colors in their eyes, and some have even been seen with two separately colored sets of horns. It is unknown what this means precisely, but since it is a feature only found on these larger, older synx, it is assumed to be connected to age. These synx have definitely not gained any speed from their size increase, nor do they get better versed in combat, however they are still considerably more dangerous. Unlike a regular synx a weeper is more then a match for a regular person, even just by using its size and weight effectively. Physically fighting one would be like fighting an anaconda that moves like an octopus. It should also be noted that once subdued, a weeper can eat something as large as an adult human with the equivalent ease a regular synx consumes a child; swallowing them up in a quick, single bite.
While this sounds like a luxury for them, synx exist in a state of nature where size is not necessarily a benefit. For a parasite: the bigger an animal is, the less threatening it is. A synx would always be more cautious of a human than a rhinoceros, even if possessing prior knowledge of neither. It is perhaps fitting that synx themselves become more vulnerable when they become larger. A weeper cannot hide as easily as a regular synx, and they quickly become the target of attack by natives and wildlife alike. Weepers are also much slower, so there is much added danger in their intrusions and escapes. Worse yet, the benefit of being able to eat people more effortlessly sometimes makes these animals far more naive and complacent with hunting. Forgetting the hazards their diet represents can be instantly fatal for a synx. Many weeper deaths can be contributed to the confusion their larger size brings, confusion that makes them start to view adult humanoids as helpless, meek children. UV exposure also becomes more problematic for a weeper. The more surface area a synx gains, the more it has to protect from this light. If exposed, the harmful effects a weeper experiences will also be hastened, making sunlight an increasingly dangerous obstacle.
Unsurprisingly weepers are an exceptionally rare sight, to the point they are even considered 'mythical' by most species and individuals. Not many synx reach this state, and most who do don't survive it very long, given the extra demanding survival skill-set it requires. The few synx who do manage surviving this way are probably the most dangerous synx of all, and something to be genuinely concerned over.