This is actually pretty similar to the style I used to make a Mewtwo sprite a long time ago.

Well, has a long time that I don't post anything...
This long time finished!
Here, Swampert, Meganium, and Typhlosion: All 100% custom:

And thanks by the tips, I'll try to apply!

Dat Thyploshion is AMAZING!

Well, they aren't 100% custom. I know for sure that charizard, squirtle and ivysaur were traced. As well as the ivysaur animation in the OP, so that makes me question the integrity of the rest of your sprites. I wouldn't be surprised if some were custom because the quality from each sprite fluctuates. Would you mind coming clean and sharing with us which ones are actually custom and which aren't so we can help you get better as a spriter?

EDIT: Reread the OP and you hint at using "bases" so I guess that's pretty much what I said haha. Well, try to group them separately. The ones that are full custom and the ones that aren't. So we can get a better read on where to help you.

Look at this and draw your own conclusions...

This is my sprite style!

For sprites like those, that's an unnecessary technique to use. It's time-consuming and you can get the same (or better) results by just having to sprite from scratch while using Swampert's image as a reference.

Also, while you got your lineart as you want it to be, you completely lost the point of everything else. Couple of jagged lines, Way too much focus on the blue colors, The yellows/oranges don't blend in properly, and little-no attention to detail.

Let's look in comparison to the true Swampert, which i assume hasn't used this technique and is the current 2D pokemon sprite version of him



If you want to get better at spriting these small sprites: I recommend dropping that technique first as it only helps for medium and big sprites.

I don't think that this technique is a time-consuming one... Well I draw in 5 minutes, scan in 2 and sprite in 15 at least...
I used this as color reference:

The sprite from D/P.
I don't have ability to sprite normally, so, I developed some techniques to take an agility on my work!
Tip computed, anyway!
Anything else?

That's one of them. You didn't say anything for the ones i mentioned specifically. If the ones you did recently are custom then cool, but I'm referring to the previous ones mostly.

I think it's a great technique to use to get the hang of lineart. And that Swampert drawing is really cute.

Something you can improve on, however, is the way you shade. Try to shade less layer-y and more roundish, like the pokémon games. If you'd like I oculd try to whip up an example using one of your sprites.

@Metal Knight: Thanks!
@Dr.Geno: Venusaur is a Edit.

Beedrill (not fully), Blastoise, and Pigeotto were traced, maybe 50% custom.

Ivysaur, Charizard, Squirtle, Serperior, Samurott and Eevee are 90% custom (I used almost the same technique of the 100% custom, but some colors and axis was taken from Brawl, BW).
Swampert, Meganium, and Typhlosion who are 100% custom.
Do you need more information?
@Steven: Oh, thanks!!! And yes, you can! Pick Swampert, since we are talking about him!

All of the darker lines in the dark blue sections of Swampert are too straight compared to the rounder ones on the real sprite.

Also incluced are some small adjustements in the outline. The two biggest problems Swampert had were an inconsistant light source, and layered shading. The shading has been adjusted to 'fix' these things. I hope you find this usefull.

Wow, Wow, Wow, it's so... wow! Amazing! It helps a lot! I'll try to make the same thing on the others!!! Thanks guy!
I'm animating Charizard, when I finish, I'll post it here!
And I'll animate this amazing Swampert! Soon...

You're welcome. Your work has a lot of potentional so be sure to keep on improvin' and keep things like theory on shading in the back of your head.

if you'd like some pokémon sketches to base your outlines off, I have some laying around in my art topic, feel free to use those.

Okay!
But now, I uppdate!
New Serperior:

I really need to animate this Swampert!
And Charizard was animated! Here:
At what speed is it better?
At This:

Or at This: