Grenades: Pass the Experience Trick
(Or who gets the experience when you "drop" a grenade)
Some commanders may have noticed that a soldier that drops a primed grenade rather than throwing it will often not get credited for the damage or killed enemies.
There is a very odd explanation for this. In order to credit the right person with experience, the game assigns ownership to a grenade. However, ownership is assigned after the grenade has been thrown, but not when it's dropped or picked up.
So who gets the experience if its dropped? At the start of a mission, all X-COM owned grenades default to the very first soldier on the transport, or the very first HWP if present. This means that if a grenade is used but never thrown during its lifetime, the first soldier or tank gets the experience regardless of actually used it.
Can we move the ownership around and pass the experience to soldiers of our choice? Definitely! Just have the person you want to get the experience throw the grenade, then get someone else to pick it up and drop it where it can be useful. Just remember to not throw it again.
The method of deployment for these grenades will be left as a practical exercise to the commander. Be creative, or be heartless - it's all up to you!
The biggest advantage of this unusual pass-the-experience technique would be to provide training for frail soldiers that would prove to be more of a detriment in combat than out of it - yet another reason for commanders to not sieve troops based on poor combat statistics.
The Funky Fire bug can be exploited to cause extra damage to units in fire per shot fired, which is arguably an exploit, and to cause additional damage to units who are standing in fire but who are not targeted by the current incendiary attack that is causing the damage, which is definitely an exploit.
Smoke grenades can be used to put out fire.
See the Incendiary topic.
Fog of War Scouting
The 3D cursor shows the terrain inside it, regardless of whether you have explored the tile or not. While the obscure shapes shown don't mean much to novice players, veterans will soon recognize tiles, and then the map segments they are native to. For example, you can easily find a UFO by looking for the distinctive wall patterns, and the power supply in the center. Or, you could use this to bombard locations such as command centers, or places you know aliens spawn at the beginning of play, with early Blaster Bombs.
The map view shows the position of all objects on the map, and updates their current state regardless of whether an X-COM unit has a current line of site to the object. And the largest object on the tile is shown on the main map for any tile which has been previously spotted. Together this can allow you to sometimes detect, and definitely determine by inspection, if an alien has woken up from being stunned, without having line of sight to the target. In multiplayer games (rare) it can be used to deduced the location and progress of opposing forces, if they pick up items from the ground.
Dead Man Switches
Grenades will only detonate when they are on the ground and when their timer has counted down. Timers will continue to count down regardless of location, but if the grenade is not on the ground, it will not explode. This means that you can set all the grenades to a time of "0" at the beginning of play, or at an earlier turn, and throw them when it's tactically feasible.
This is a double-edged sword, however, because should a unit fall dead or unconscious the grenade will hit the ground and promptly take out anything in the near vicinity... which may (or may not) work to your advantage. This tactic encourages keeping your troops far apart. If you anticipate the soldier will have a very high chance of being killed, it may be wise to use the "pass the experience" trick as described earlier before handing the soldier an armed grenade. However, it can be exploited against Tentaculats: give a soldier two armed grenades. If he/she is caught by a Tentaculat, the grenades will drop. The first will kill the zombie while the second kills the newly formed creature. Could also be used with proximity/PD grenades. This will not work against Chryssalids because the second grenade will be destroyed before detonation, whereas in TFTD, explosives cannot be destroyed by other explosions.
As it is possible in reality to carry two grenades with the pins removed, on a very short fuse setting, holding them by the spoons (with the fuse not starting until the spoons are released), this is really only an Exploit if used with grenades other than those held in the hands, or large explosive packs. (Alien grenades could feasibly have a similar mechanism - it's actually a good safety feature.) Even then, for small numbers of grenades (4?) it's probably doable, if one were suicidal enough.
Defusing Proximity Mines
If your proximity grenades' locations have become inconvenient, all proximity mines on the Battlescape can be defused by saving, quitting the game, restarting it then reloading the game. You can still drop on top of them with a flying suit, or by dropping from a hole in the roof in order to safely pick them up.
Fixes are available for the underlying bug, which can also be fatal in a situation where you are relying on proximity grenades to work correctly.
Base Defence Mission Spawning Issues
If there are too many soldiers and/or aliens in too small a base, their initial spawning is unusual. Soldiers can spawn in the Access Lift and Hangars. Aliens can spawn outside the Access Lift and Hangars. Some lifeforms may not spawn at all.
Why does this happen? Each base facility has certain hardcoded spawn tiles. The Living Quarters, for example, have 8 spawn tiles, 7 on the lower level in an "H" pattern, and 1 on the upper level. Soldiers usually spawn at these spawn tiles, semi-randomly outside the Access Lift and Hangars. Aliens are assigned the spawn tiles within the Lift and Hangars.
But, if the number of soldiers exceeds the number of "friendly" spawn tiles, the excess soldiers will spawn at the "alien" spawn tiles inside the Access Lift and Hangars. Similarly, if the number of aliens exceeds the number of "alien" spawn tiles, the excess aliens will spawn at the "friendly" spawn tiles in the rest of the base. If there are not enough spawn tiles for the sum of soldiers and aliens, then some lifeforms will not spawn at all. Soldiers have higher spawning priority than aliens, so aliens will be the first to go (fail to spawn). All weapons and items will still be generated, though.
This can be exploited by garrisoning a base with so many soldiers that all spawn tiles are used up. Zero aliens will spawn (but their toys will still be generated), resulting in a bloodless victory and millions of dollars of loot!
A radar base with one Large Radar or HWD, an Access Lift, and one Living Quarters, can be filled up with 22 soldiers.
But if this is considered an exploit, then what is the "ethical" thing to do? To get all aliens to spawn properly at a radar base, you would have to go out of your way and build a hangar. This would in turn affect your defence tactics, and cost you money. If you don't build the hangar, you need to recruit at least 25 armed soldiers (with the accompanying Living Quarters and General Stores), or else a Sectopod or Chrysallid will probably spawn behind friendly lines. At that point, you could argue that the computer is the one doing the cheating, and 25 soldiers seems excessive for a radar base. On the other hand, you would be fighting a reduced number of aliens, since the Access Lift only has 8 spawn tiles.
Also, you can only have 40 "units" where a soldier is one unit and a HWP is 4.
Maybe you should just shoot down the scouts.
|Spawn Tiles on Lower / Upper Floor
|5 / 3
|15 / 0
|7 / 5
|7 / 4
|HWD or Large Radar
|5 / 1
|Lab or Workshop
|6 / 1
|7 / 1
|4 / 5
|Defences (non-missile) or Shields
|5 / 1
|7 / 3
|0 / 2
Due to questionable AI, aliens will not fire at you through an elevator (either up or down), even though they can see you and you can see them. When approaching elevators, have a soldier stand on it at the end of the turn, even if this leaves them with no TU. The aliens will not be able to come up/down through the elevator, keeping you safely shielded while you bring up rear troops and prepare for a floor breach. Additionally, soldiers may be able to see aliens standing at/near the elevator above or below them and can fire on them from the safety of their "elevator shield".
Risk Free Milking of Alien Bases
This experience training and (optionally) booty-gathering exploit relies on the "Elevator Shielding" exploit. When assaulting an alien base, your soldiers will be deployed at two staging areas with a 2x2 elevator in each one. Block all eight elevator squares with a soldier and wait for the fun to begin. Just keep skipping your turn and eventually, the aliens will find your soldiers and begin to congregate under the elevator. You can now shoot at them with complete impunity and can even pick out specific soldiers who need Accuracy training. When you see that no more aliens are appearing after a few turns, get your solders onto the evacuation area and leave. The alien base is intact for you to return for additional practice later. If you happened to kill everyone the base will be destroyed, so watch the timing of the alien movement phase and take care not to kill everyone (in practice this means 'save regularly', since there is no in-game way to determine exactly how many enemy units are left alive). However, the alien leader or commander will almost always stay in the command center, so this is usually not a problem. For best results, arm your soldiers with pistols to maximize the number of shots they can take on each alien. Also, it is not recommended to attempt this tactic on a Sectoid or Ethereal base unless you are very confident of your soldiers' psi strength. As an extra bonus, you can collect alien weapons and equipment before evacuating. It is worth noting that this "shield" does not prevent aliens firing a Blaster Bomb up the lift shaft. However, unless you are running a version of the game that fixes the Vertical Waypoint Blaster Bomb bug, such attacks will rarely succeed - mostly they will explode on the level below, with no harm to your troops. So unless you have fixed the Vertical Waypoint bug, there is minimal risk with this exploit. But as it is a cowardly and egregious Exploit, fix the Waypoint bug, or better yet, just don't do it.
Panicking Alien Location Exploit
Whenever a soldier or alien panics or goes berserk from low Morale, there is a message given to the player stating what soldier or alien has done what. As well, the screen is centered on the unit that has failed it's morale check. At times, this will allow sharp-eyed players to locate aliens who have panicked in areas you have already fought, by displaying the location of the alien who has lost their cool.
Relaying and Sharing
A set of related Exploits arise from the TU system, and the fact that it allows the sequential execution of tasks by different units that really all should be occurring simultaneously, in parallel.
Many consider this simply a tactic and don't think of it as an Exploit, but measured against realism, its use anything other than very occasionally is an exploit. Simply, a grenade can be primed by one soldier, then thrown between any number of soldiers before being finally delivered to the target. While it is desirable to be able to throw already-primed grenades, for the well attested (but dangerous) practice of throwing a primed grenade away from friendly troops, using this to cover the battlefield with leap frogging grenades is an exploit to circumvent the (high) TU costs of priming grenades and the (minimal) encumbrance costs of carrying grenades, and is a way of 'concentrating' TUs from safe rear units toward exposed front line units. A number of self-imposed rulesets require not using this tactic. Or rather, this exploit.
Weapon Use Relay
A less obvious but more obviously bizarre variant of the grenade relay is a weapon-use relay. A weapon can be fired and then thrown to another soldier who fires it again, then throws it to another soldier, and so on, without limitation. There is no reason why an entire squad could not fire the same weapon in the same round, possibly multiple times each depending on the specific weapon's TU costs. This will then greatly exceed the normal maximum rate of fire of this weapon, as well as being patently ridiculous. Scenarios where this would be advantageous would be any time that effective weapons against the enemy are in short supply in inventory. Particularly effective with weapons that do have unlimited ammo (lasers, stun rods / tazers / drills).
Equipment Use Relay
The same technique can also be used with Psi-Amps / M.C. Disruptors to allow part or all of the squad to get at least one Psi/MC attempt from just one device. And it can be used with Medi-Kits to exceed the normal limit on healing (etc) per turn. It can also be used with Motion Scanners / Particle Disturbance Sensors to achieve excellent triangulation of signals while only having one such sensing device on the mission.
A variant of this technique can be used when ferrying loot, corpses, casualties or equipment back to the transport / exit area during a planned (or unplanned) abort, for example during alien base/colony raiding operations. One unit picks up some heavy objects, and moves with them (some times it is more TU-efficient to throw some objects, depending on the unit's strength and object's weight). Before the end of the unit's turn it throws the object forward, or drops it and moves off the square, so that another unit can continue the Loot Relay during the current turn.
There are two advantages. First of all, as with the other related exploits, all the squad's combined TUs can be pooled onto a single operation that really should be limited to 100% of one unit's TUs per turn. Instead you can use as much as 1000% TUs per turn, or more, moving a set of heavy objects right across the map in one turn at speeds far faster than should really be possible. It's the equivalent of FTL travel for Battlescape loot.
The second advantage is to ensure that no one (or as few units as possible) involved in the ferrying process begins or ends their turn holding the heavy objects. This then avoids the significant TU penalties for being encumbered, which only kick in at the beginning of the next turn. It is often more efficient for the last link in the ferrying chain on a given turn to wait over the ferried objects, and only pick them up at the beginning of the next turn, thus having many more TUs to move them forward to the next link.
The ferrying units should be set up in a "fireman's chain" type of relay. This in itself is not an Exploit, just a good tactic that works in reality. The difference is that by exploiting the TU mechanics, it's as if a chain of ten people could suddenly all run/throw ten times faster than normal.