YMMV / X-COM: UFO Defense

• Demonic Spiders: All of the terror units, other than the Reaper and Silacoid, fall under this. Two in particular though stand out:
  • The Chryssalids are without a doubt the most feared aliens in the game, invoking panic in even the most hardened and experienced player. They have only a melee attack, but their fast speed ensures they can easily make it to their target. The bite itself dosen’t do much damage, but it is the effect it has on humans that makes the chryssalid so dangerous: it turns them into a zombie. Not only does this equal instant death for the X-Com operative, but when the zombie dies a Chryssalid takes its place! If you aren’t careful, half of your squad may get turned into zombies, each of which will be yet another Chryssalid to deal with. Worse of all is that Chryssalids are a terror alien which means, unless you ambush their ship, they are going to be on a map with civilians which can all be turned into Chryssalids! Thankfully Chryssalids become much more manageable late game after you get flying armor, allowing you to float and completely avoid their biting attack. They are also vulnerable to explosives.
  • While the Chryssalids have the lion’s share of infamy, not even they are the most dangerous terror unit in the game; that would be the Sectopod. These hulking metal monstrosities are armed with a powerful laser that makes short work of even heavily armored units, has incredible reflexes, and are so heavily armored most weapons can’t even hurt it! Thankfully their one weakness is laser weapons, perhaps the most common type of weapon in the game. Plus even they can still be taken over by psionic soldiers and can be affected by low morale.
• Game-Breaker:
  • Powerful and highly skilled psionic troopers take the game balance and blow it to pieces. When you have powerful psionics (>90) with a high skill level, they can mind control pretty much every enemy from anywhere on the map with 100% success. Even a single psi trooper is extremely powerful, as you can use aliens as expendable scouts, and cause havoc by controlling terror units. But the fun doesn't stop there. With a full squad of psi troops you can use aliens as scouts and chain mind control them without risking any of your soldiers. Under certain circumstances you can even manage to mind control every alien on the map on your first turn, without even leaving your ship. High ranking enemy with a Blaster Launcher? Mind control him, and force him to commit suicide while wiping out a bunch of his friends at the same time. Want to scout a load of the map? Mind control a Chryssalid and put his speed to your use. And then mind control an armed alien to shoot him when you've no further use for him. You don't gain any stat increases from shooting mind controlled units, or causing friendly fire, but by this point you won't need them.
  • The Blaster Launcher is the last word in BFGs in this game. Able to fire a Player-Guided Missile, it's entirely possible for this monster of a gun to be fired from within the Skyranger, sent on a path with up to nine waypoints, and into the heart of a UFO. It's capable of blasting holes in UFO hulls and the blast radius is absolutely huge. Plus, it can solve the tricky issue of indoor combat; Why bother clearing out a shack room-to-room when you can just level the whole building?
• Good Bad Bugs: In the first game an overflow bug in the save files can cause new items to appear in storage. This is notable for being the only way to obtain the "Alien reproduction" item without deliberately modifying the game.