Due to being mostly reptilian you have the ability to sense other creatures by smell and body heat.

You are proficient in Perception and gain advantage on Perception checks when it relates to trying to sense other creatures that emit either smell or heat/cold.

Although Mwellrets are fast creatures they are also intelligent hunters, so why chase your prey when they can give themselves willingly? 

Once per day you may use the spell Charm Person to lure in the little peoplesss. The target may only be your size or smaller. You regain this ability after a long rest.

Mwellrets are from the deep swamp and quite often their prey was much larger and stronger than them so they learned a single scratch can kill so they would attack then stalk them from the shadows until the venom takes the target.

Instead of an unarmed attack you scratch with your venomous claws. on a hit the target must make a Constitution save DC 10 + your Constitution modifier. on a fail they take 1d6 Poison damage and are 'Poisoned' for 1 minute on a successful save they take half damage and are not 'Poisoned'.

Living in the deep swamp means never being at the top of the food chain so Mwellrets had to grow up knowing being faster could mean life or death.

+2 DEX and proficiency with DEX saving throws

Mwellrets secrete a pheremone that affects creatures cognition and makes them more susceptible to their persuasions.

+1 CHA and proficient in persuasion.