Hover over the different seed/zombie packets to cycle through the corresponding sprite's costumes. Switching will reset the frames (set the costume back to 1). You can also adjust the FRAME SPEED using the top-left slider. It's set to 0.2 by default as that's the speed used for my own PvZ DS game currently.
Play the actual Plants vs Zombies DS game here: https://scratch.mit.edu/projects/723313433/ Since I'm creating a PvZ DS game, I figured I might as well share the sprite costumes for those looking to take them easily. Will update as I add more plants and zombies to my game. Sprites (mostly) gotten from the Spriters Resource, which were taken from the original game. Give credit to Popcap, not me lol.