It's not hard to switch between them at all. All you need to know are the huge differences.
*Dogy's Off-the-wall-but-very-accurate-reference: Think of it as switching between Ken and Ryu in just about ANY SF
-Note: Sorry, I kinda realize I started this with the Doc-to-Mario comparison.-
Differences between Doc and Mario:
1) Mario's aerials have less lag than Doc's. L-cancelled or not.
-Normally a frame or two.
-This is important because when you play Doc, you can't come out of stuff as fast as Doc.
**THIS IS NOT TO BE CONFUSED WITH MARIO ATTACKS FASTER THAN DOC. He can do more attacks, but his attacks COME OUT at the same speed**
2) Mario's F.smash is completely usable for zoning, where as Doc's really isn't.
-This alone makes Doc's harder Matchups (Marth, Sheik, Falcon) easy for Mario.
3) Mario has capelift, Doc only has capestall.
-So that means Mario can do SH Cape -> Aerial, where as Doc can only do SH Cape -> (perfect)Waveland.
*Note: Doc can actually do SH Cape -> Aerial, but he can ONLY do a 1 frame n.air.
4) Mario's u.tilt is actually worth two flips. Doc's is just a "go away" kind of thing. (More often than not)
-This is pretty much THE main reason why Mario can combo the crap out of stuff and Doc can't.
5) Mario's u.smash is (at times) a usable kill move, where as Doc's has a double standard.
-If Doc upsmashes somebody on the ground, it hits with the meteor smash animation. If he hits them in the air, it's a regular hit.
6) Mario's fireballs are more of an offensive projectile, Doc's tend to be defensive.
-Both of them can do THE EXACT SAME SHENANIGANS with their projectiles. -glares at eggz-
-Mario's fireballs follow the decayed height rule (If you throw from FH, it bounces at SH, sh to ground), where as Doc's Pills bounce to the same height.
-This makes it easier for Doc to control airspace with his projectiles, making some of Mario's more difficult matches easier (Jiggs)
7) Mario's recovery is better than Doc's.
-Mainly because of Capelift vs Capestall.
-Also the obvious Mario can frickin walljump. XD
8) Mario's jab combo can be a legit mixup, where as Doc's tends to be a gimmick.
9) Mario, overall, has less KO power than Doc.
-I personally don't think this matters if you're good at gimping, but if you just flat out need KO power, then yeah, you'll get more with Doc.
10) Mario's n.air is strong-to-weak (normal), where as Doc's is weak-to-strong.
-Mario's tend to send people off stage with N.air. You're not going to be doing alot of that with Doc unless you get your n.air out there for a while
11) Forward airs.
*I'm only adding this for good measure. It's kinda obvious.
12) Capes.
-Doc's cape has more HITBOXES (not reflect boxes, HITBOXES) than Mario's.
-BOTH ARE THE SAME LENGTH, (Doc's is just "wider")
-Both have the same reflect box.
13) up+b wall jump and up+b cancel.
-stuff-
That's really it off the top of my head. I started kinda ranting on on some obvious stuff.
But the big thing is, note the stuff I didn't say.
No false bs about Mario moving faster or jumping higher than Doc, and nothing about Doc being heavier. A lot of people think that kinda **** is true.
There are absolutely no character mechanic differences between Mario and Doc (save walljump), only move properties.
That means if you were to go whatever practice mode you do, and just maneuver around a level, it's going to feel EXACTLY THE SAME.
____
.... Does that answer your question? ^_^
From what I;ve seen of recent matches, his Mario is pretty fail-sauce. Not to say I WOULDN'T get 3 stocked by M2K, but I agree with PM. Play your own style. I've even had d-tilt work in my style, albeit poorly, but that just goes to show each player, especially with Mario, has differnt tastes and styles.
