Mission 20: Destroy the shadow globs
Shadow globs have overrun Twilight Town. They have been deemed harmless at present; however, allowing them to propagate further could have dire and unpredictable consequences. Destroy them on sight.
Roxas is sent out on another mission. As he finishes this one, his name is called, and he is overjoyed to find that Axel has returned from his mission at Castle Oblivion, safe and sound. During their ice cream treat, Roxas tells him about his new friendship with Xion.
Prepare for this one by bringing magic, as much as you can carry at this point. Some globs are impossible to reach at this point in the game, and magic will be the only way to take them out. You'll fight other Heartless along the way, but the blobs don't attack themselves. Most of the Heartless are pretty weak, save for the Guardian in the Tram Common. Locations are listed below.
Once you get enough to complete your mission (or try for all of them), you can RTC.
If you can't quite make it, coming back with abilities such as High Jump and Glide to make this one easy as pie.
Equip Roxas with Fire spells, using Doublecast, Triplecast, and Quadcast panels to give him plenty of castings along with adding it as a shortcut to be able to use it quicker. Also, equip Hi-Ethers and the Haste panel (which can be obtained by redeeming ten Challenge Sigils at the Moogle Shop). Glide can also help here. Instead of attacking the Shadow Globs, move to central locations and cast Fire spells to wipe them out. Ensure that other Heartless don't get in the way by using Lock-On. The only hindrances are both the tightness in time and trying to destroy each Shadow Glob with only one fire attack. Also try to only go for Shadow Globs that are easy to destroy without going too far once you are at the Tram Common to be able to get back to the starting point on time.