No probs. So indegenous alien life in the games context means alien creatures that live on this planet.
My philosophy on enemy design is think of the enemy behaviour first, and then think about how you will design how it looks.
Enemy behavior is informed by what the player can do. And in the case of metroidvanias, that behavior is changing throughout the game. So for example, if you give the player a wall jump move. Maybe you will design an area that first teaches the player how wall jumping feels with no risk level layouts. Then introduces an enemy that sticks to a wall but doesn't move to give the player an easy-ish test. Then you would place enemies that maybe stick to a wall but move along it rhythmically. Not very creative example but you get the idea.
Once you are happy with the mechanics of the enemy, and you know what telegraphs it needs, you design how it looks. That's how I do it anyway. That way I can make sure the enemy and its attacks will be readable, and will offer a counter challenge to the players new moveset.
For example in my game, Feed IT Souls, I introduced a new tentacle enemy that sticks to walls and can't be killed with a projectile once you get that powerup so that the difficulty ramps up and counters the newly acquired skill. It's the exact same behaviour as a precious enemy (as in its just there to be an obstacle while wall jumping), but this time you can't get rid of it with the new projectile attack.
In summary, Player moveset informs enemy behavior. Enemy behavior informs that enemies GFX.