Big-Lipped Alligator Moment: During Papes' interview on The Moe Show, he refuses to tell Moe anything. Suddenly, Shirkit comes out, and Papes asks what she's doing there. Shirkit then apologizes and leaves.
Evil/Iburu is the Greater-Scope Villain of the first two games, the Big Bad of the third game, and the orchestrator of everything bad that happens. Seemingly enslaving Ogura at a young age, he tells Ogura to destroy Pufftop and, when he fails, gives him " another chance" in the form of painfully transforming him into an Eldritch Abomination. He attempts to execute Moe before his father preforms a heroic sacrifice, but Evil doesn't mind this outcome. At the end of the game, Evil discards Ogura after he is no longer of use to him, claims that he's going to destroy the entire universe, For the Evulz, and very nearly succeeds. A psychopathic, seemingly invincible demon, Evil is a far cry from the lighthearted, sometimes even tragic villains of the past games.
Mashtooth, the Big Bad of the 5th game, is the cruel leader of a gang of Space Pirates and desires nothing but power. Chronologically, the first thing he does is invade the peaceful planet Bunnera to suck out the essence of its inhabitants, simply to make him stronger. He discards of the smaller Bunnerans, claiming "these snack-sized Bunnerans have given me enough power, but I need more." Mashtooth then goes after their prince, who narrowly escapes with his life. In the final battle, after his subordinates pulled a Heel–Face Turn on him, he eats the prince, who is still alive inside him, and uses the moon as a battering ram to try and kill Starfy, and possibly hundreds of thousands of innocents in the way. Ruthless, cruel, and terrifying even to his own minions, Mashtooth stands out in this relatively lighthearted game as a tyrant who would stop at nothing, just to satiate his lust for power.
Crowning Moment of Awesome: Though it involves a truly aggravating sequence of Button Mashing, singlehandedly pushing back the moon and then using it to take down Mashtooth in 5 is by far the most awesome thing that Starfy has done in the entire series.
...until in the 5th game when you're trying to get that 9,999-pearl clothing item, and especially when you're trying to get all the toys from the Gashapon machine (which replaces the previous games' system of simply defeating an enemy to add it to the beastiary); the toy you get is completely random to point where it's possible to get duplicates, thus eventually forcing players to resort to "farming" (itself a subversion in which you just have to collect the pearls) in order to get all the collectibles, making this particular entry in the series an inversion of this trope.
Also, while the main game is a nice, relaxing platformer, stage 10 is Time Attack. You can't even fight the Boss until you beat a certain time goal on each stage. The boss has an extremely hard-to-dodge attack that does infinite damage.
Every New Game+ in the four games has tweaked level designs, trickier bosses and some Nintendo Hard extra levels. The True Final Boss of 3 is a pain, having 12 hard to reach weak spots, moves quickly, and has a final attack in which you must hit 12 random weak spots on a meteorite before it crushes you... and then you'll have to try defusing the exact same attack again. Oh, and you are limited to 5 HP during boss battles. Sorry, no health upgrades before the fourth game.
That One Attack: Evil's Wave MotionPuke is absurdly hard to deflect, you have to repeatedly hit the crosshairs precisely over and over again just to slow it down, should you failed one of them, all you can do is to wait for the inevitable One-Hit Kill to claim your life.
Ogura's own Wave Motion Gun attack moves faster than you, can turn its direction around with no telegraph and lasts for a very long time.
And Old Man Lobber's one hit-ko Clakkity is ridiculously hard to dodge, and does infinite damage. Good luck...
That One Level: Sogwood Forest in Legendary Starfy. It's full of poison pools that are difficult to get out of should you fall in them, bobbing chestnut platforms that are hard to leap from, and several levels have you swimming upwards through constantly falling dewdrops. The worst part is, to get maximum height while swimming through the dew, you need to launch from the water with a Super Star Spin, which can cause serious Damn You, Muscle Memory! moments.
The Woobie: Moe. His family is forced to move from their home, his mother dies, and then when he meets his dad, he makes a Heroic Sacrifice that kills him.
Ogura also counts. He was seemingly enslaved by Evil at a young age, and is hurt by Evil when he loses to Starfy, despite secretly respecting Starfy he can't show this because Evil would kill him. Makes it all the more sadder when he performs a heroic sacrifice to elmininate Evil.