When I write a dex entry I do it about the following aspects, so it's up to you to think of what makes the Pokemon more distinctive:

• Habitat
• Relationships with other Pokemon
• Relationships with people
• Personality
• Unique powers
• Food
• Battle prowess and strategies
• Rumors, myths and lore about it.

can you have a look at my very old pokedex entries... & see what you think of them? this is before i got them changed, mind you :>

aibyou:

Spoilernormal/water

old pokedex entry: it lives in fields, by rivers
it can also be kept as pets
it can be shy sometimes

Stakitty:​

Spoilerelectric

old pokedex entry: they live in safari's

they are really playful, and don't know their own strength sometimes

they show affection for each other & other people by using nuzzle, but it ends up shocking people (not their own kind, though, because they like it)

when they get hugged too tightly, they tend to use charge

pikinu:
Spoiler ​

electric

old pokedex entry: it can normally be kept as a pet, but it can also be caught in the wild
it has really good hearing and good eye sight, so if it sees anyone suspicious, it will run away

they are very loyal to their owners

ambfox:

Spoilernormal/dark

old pokedex entry:

it can be kept as pets
but it also lives in the mountians
it's said that when there's a eclipse, they use the moon shape on it's forehead as a flashlight
also, they use their moon shape, legs & tip of their tail to light up any room when it's dark

beta version of chuling: aenka

Spoilerice/flying

pokedex entry:

he lives in fields

he likes to eat berrys, pokepuffs & other food, he doesn't really like fighting much when he doesn't have to

he likes it best when it snows, but he can withhold mostly any weather, but he hates rain

when he's happy, he does a little squeak & does a flip and flaps his wings a little bit at the end of the flip

but when he's not feeling very happy, he let's out a high pitched squeak, but he calms down when he's petted on his tail

when he's not feeling very well, his fur sticks up a little bit & every now and then, he lets out a little stream of snowflakes from his cheeks