Title screen

The Doki Doki Panic screen starts off with three balloons, and each balloon pops and shows the title logo.

Intro

Doki Doki Panic's intro sequence is this: Two kids are reading a book, when a big green hand pops out and yanks them into the book. Their pet monkey runs off to find help. A family finds the book, then decides to jump into it and save the kids.
In Super Mario Bros. 2, the intro is just a story about how Mario dreamt about some weird land. Not too exciting.

Character Select screen

In Doki Doki Panic, you choose your character at the start of the game and play all the way through with him/her, saving after you defeat a boss. So basically there are four save files, one for each character. In SMB2, you can pick your character after every level.

Bonus Chance

DDP's Bonus Chance screen is incredibly bland. Even though SMB2 used its Title screen as the background, anything's an improvement over DDP's screen. The cool thing about DDP's bonus chance is that the vegetables change depending on what level you're in. This would've been neat in SMB2, but, oh well.

Mariofied

These are all the items and characters that were changed from DDP to SMB2. The enemies were not changed, except for boss of 5-3.

The Lost Mouser

Doki Doki Panic originally had three Mousers, the third one appearing at the end of World 5-3. The white Mouser was replaced by Clawgrip, a rock-throwing crab.

Above is a map of the third Mouser's chamber, which was completely replaced by Clawgrip and his stockpile of rocks (below). The four clumps of grass to the left of Mouser were bombs.

Comatose sprites

In Doki Doki Panic, not very many items were animated. For example, there are no animation frames for Cherries, POW Blocks, vines, grass, Crystal Balls, Bomb fuses, water, and spikes; the animation for these items were added for SMB2.

The Albatoss enemy also has fewer animation frames than its SMB2 counterpart. Phanto does not move when you pick up a key, but he magically appears later to chase you around.

In a somewhat related note, if you get down to one dot on the power meter in DDP, you don't shrink to half your size. This and the "B-Button run" are Mario trademarks, and were duly added to SMB2.

Audible changes

• 1-Ups make "finish level reward fanfare" noise
• Enemies make different noises when picked up/thrown
• Birdo makes different noises
• Rockets makes different noises
• POW Blocks make different noises
• Cherry collection makes different noise
• Doors/potions make different noises
• Mask gates make different noises
• You make different noises when hit
• Starman and Sub-space music is different
• Whale's waterspouts make new gushing noises
• Stop-watch noise is slightly different