* CreepyCute: The Grinning Darns fall under this for some, thanks to the SuperDeformed graphics of the games (the official art makes them look more creepy than cute).
* EnsembleDarkhorse: O2-Joy is the most popular Darn Army member, thanks to his unique design and creative boss fights. It helps that he's the only non-Rilo member to be an end-stage boss in both games.
* GeniusBonus: In the first game, O2-Joy's theme music is a minor-key version of the Ode To Joy.
* SurprisinglyImprovedSequel: Aside from well-designed and fun boss battles (especially the last one), the first game is a decent if unremarkable side-scroller. The sequel is a top-notch ActionGame with incredible pace.
** Any attack that produces arcing impact debris in ''Devolution'', since it's hard to tell where it will fly and it can't be shielded. If a boss has an attack that produces this (Rilo's/Xoda's ground blasts, [[spoiler:Tango Source]]'s Air Show and Sports channels, [[spoiler:Penultimate Tango]]'s yellow diamond attack, [[spoiler:Ultimate Tango]]'s axe slam, and [[spoiler:Waltz]]'s energy balls), it'll almost always be the toughest attack to dodge in their arsenal.
** Watkins is the toughest member of the Grinning 4 thanks to his molotov cocktails; he tosses three consecutively, and they arc and create ground explosions. Fortunately, Watkins in a GlassCannon and will last for less time than any of his partners if attacked when possible.
** Omega Darn from the first game is utter chaos in boss form, with the player constantly having to switch between their different forms. And it's very easy to accidentally switch when you didn't mean to and take a barrage of lasers or homing missiles right in the face before you can switch back and dodge. Not to mention that eventually the boss adds a screen-filling attack to its arsenal that deals massive damage, and the only way to avoid it is to hit him with a missile before it activates or desperately throw yourself against another, less-damaging projectile to take advantage of your MercyInvincibility.
** On higher difficulties, the [[DuelingPlayerCharacters Rilo/Xoda]] battle in ''Devolution'''s Level 3. You're fighting an extremely fast, tiny target that can attack from many directions, and not many of those attacks can be shielded. The Xoda fight is more manageable since you can fire at her from afar with Rilo (though her unique attacks are stronger than Rilo's carpet-bombing), but Xoda has to get up close to attack Rilo, which makes it easier to get hit by a gunshot or debris. Fortunately, you only have to reduce the other character's health bar to half before the Sea Serpent hijacks the battle.
* ThatOneLevel: Level 3 in ''Devolution'' is extremely chaotic and a huge step up from the first two stages. Swinging axes coupled with Darn Kiminos dropping ball 'n' chains, the Darn Kappa bridge, the underwater segment with limited movement, the bamboo rising from the ground as you speed through the last part... there's a ''lot'' to pay attention to. Fittingly, [[ThatOneBoss Rilo/Xoda]] is at the end of the stage.