These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
That One Attack: Any weapon that instantly hits you the moment they're used. To use them on enemies is very satisfying, but to have them used against you means that even retreating from them isn't a guarantee.
Lava Palaver: Another Timed Mission where you're base is destroyed, and you can only use a Medic to bring aliens called Ikemen to a transporter. But that's not all! Two Baddie teams are hunting you down, and there's lava everywhere. Which is bad because the Ikemen you're holding might randomly fall out of your grip into their demise. Finally, the teleporter can only take one Ikemen at a time and must be recharged with 4 lamps for each transport. You'll likely waste more time fighting off the Baddies and figuring out how to reach some of the Ikemen than you will saving them.
That One Boss: The MegaMech. The Final Boss of Single Player mode. You fight it on a level full of lava and automatic turrets, and if you get too close to him, it attacks you with several different weapons in the game at once. Damaging it constantly makes it release the 8 Baddies powering it, all ready to murder you with lasers. They can't be killed until the MegaMech itself is destroyed, and will eventually return to it. On top of that, it can recharge itself when its health gets low. So you have to destroy 4 towers that do this, but only after finding the ride teleporter to do this, and even then, the MegaMech can quickly rush over to squish you and carry you away from the towers, laughing at your expense before barraging you more. Even your Mission Control doesn't believe you can beat it. Have fun.