Is there a way to sort what Common Rare Epic and Legendary units are?

[XenosHg]

As far as I can see, there is no visual difference between Common Rare and Epic and only maybe Legendary are yellow.
And how rare are these rarities?
It's kinda hard to plan even the most basic strategy when I am hoping to get a vampire lord and I have 50 bats but the chance of getting one is 0.5% and I just never get a single one in a whole run.

[Selegun]

It's not explained well but the minions have different boarders on their cards to represent rarity. Grey boarder is Common, Light Blue is Rare, Purple is Epic while Legendary is Yellow.

Don't get hung up on trying to pick up a single monster. There are a ton of combos that hit far, far harder than Vampire Lord and take less setup to get rolling if you can blunder into them.