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.
Pay more attention to the dialogue: it's been mentioned that Miwa grows exceptionally fast in a few months because Michio had injected Festum antibotics to pilot the Mark Eins, and these Festum cells are also inherited by her, altering her growth (which also happens in the movie, though that period is one year). Also, if Michio is alive, he'll comment that no matter what happens to Miwa, she's still his and Yumiko's daughter, so it's not an intentional fault.
Dialogue also states that Michio injects the Festum antibiotics after Yumiko has already been pregnant for a while, most likely since Scenario 26. Before the battle begins in Scenario 37, Michio has the Festum antibiotics injected because his Cynadetic Code matching with the Nothung Models has decreased due to age.
Any Festum successfully hitting an allied unit drops the pilot's Will and armor value. While these Standard Status Effects aren't such a big problem, the "demonic" part lies with all Festum units having an ability that grants them greater accuracy and evasion rates against non-Fafner units (and Heroman, despite his size rating).
Individually, ELS units aren't strong, but they come in large numbers. Alongside dealing normal damage to HP, they also absorb EN, at a minimum of 10% per attack. UX treats the case that if any unit's EN is rendered to zero by an ELS, it is automatically destroyed.
Fix Fic: This refers mostly to the Gundam00 movie's story. During the story Mr. Bushido can be saved from dying in combat. Setsuna does not join ELS meaning he will not be separated from the people he loves for five decades.
Good Bad Bugs: UX has notably plenty, such as if you bench a character for two scenarios and put them back in and make one kill, their kill count is multiplied by over fifty (the amount decreases over time). On subsequent playthroughs, kill counts are naturally multiplied, making it potentially difficult to keep track of how many kills you need to unlock secret characters.
There's also a few game freezing bugs, such as one attack from Ryofu Tallgeese and any allied unit counterattacking following an enemy attack. Also, by attacking Master Therion with the Shining Trapezohedron during the Demonbane finale, if he counterattacks with his own Shining Trapezohedron, the game will freeze (this may double as an Easter Egg because it's the result of the bad ending from the Visual Novel). During Scenario 34, if you use the Triple Dog attack after the Linebarrel changes into Amagatsu, the game will crash if you don't skip the battle animations; likewise in Scenario 43, the game will crash if battle animations are not skipped by using the Gim Gene All-Attack after Nero deploys.
Once the Deus Ex Machina reveals itself, all characters except Kaidou and Magami get a reduction in Will; instead, these two gain +30 Will or are completely unaffected. This occurs if you Wing Cross before Deus Ex Machina deploys.
When you give a character the pilot skill "Foresight" note Automatically cast the "Alert" Spirit Command each turn and pair them with an ally in a partner unit for the first time, at the start of the next scenario, Foresight will also activate on the other unit, though this only happens once. It can happen on subsequent playthroughs too, including any partner units that have been paired for a while. This particular bug seems to occur randomly.
Also, despite "Foresight" activating during the player's turn for the pilot who has the skill, it may stop activating at some point in the game.
Soushi's Spirit Points will sometimes become infinite and no matter how much you cast his Spirit Commands during a scenario, he won't lose any.
By restarting a scenario and placing Ruri Hadou as a Tactician before and setting another character as a Tactician who is a sub-pilot (or even the primary pilot of a multi-pilot unit), their Spirit Points will increase by 20 due to Ruri's Tactician Bonus. However, this effect stops when you cast one Spirit Command, rendering their Spirit Points back to normal.
Following the second playthrough of the game, characters may stop gaining experience points from successfully destroying both enemy units in a partner unit. This also applies to MAP attacks, where you only gain experience equivalent to one enemy being destroyed.
If Agnes Berge or any pilot forced to deploy for the next scenario is paired with another character that's a lower level, a Level Scaling bug occurs where enemies will scale to the latter.
Ryofu Tallgeese calling Yulianne a shallow woman and saying if she wants the proof of life that much he'll give it to her, que him yelling soul and Yulianne going "Noooooo!!" Chousen says to not give misunderstandings to people.
Shinn Asuka, the pilot of Fafner Mark Destiny.note Post-Mobile Gundam SEED Destiny Shinn, who lost Stellar Louissier and Rey Za Burrel by canon, becomes a mentor figure to the Fafner cast in UX, especially to Kazuki Makabe. Since SEED Destiny and Fafner has the same character designer, along with Shinn's SEED ability (which looks awfully akin to the assimilation effect for late-Fafner Kazuki) and his Destiny Gundam, this makes him a perfect Festum buster like the Fafner pilots. It doesn't help that all events involving his Destiny Gundam (got damaged, receiving the repaired Destiny, and revealing his Combination Attack with Lunamaria) in UX happened on Tatsumiyajima.
Shou(ko) (Ha)zama, the female Aura Battler.note If you fulfilled requirements to reacquire Shouko Hazama, after the sequence where she self-destructed to destroy the Festum in Scenario 13, she'll be brought to Byston Well (where the cast of UX are coming back from) instead, and continue to fight for the people there, even being called a "female Aura Battler" (which is a sign to see if she's rescued or not). The kicker? Her name can be broken into that of the above, in line with that of Shou Zama, the male lead of Aura Battler Dunbine.
Setsuna has matured since the second season, moreso in the movie, and Lockon Stratos does lampshade the fact that "Setsuna can't call himself Gundam again" when they first met.
That One Boss: Don't let the full recovery event fool you, but Kali Yuga is probably one of the hardest bosses for SRW handhelds. First off, all of her attacks inflict status effects (one of which will halve your pilot's stats), meaning without someone like Fei-Yen HD using her Tactician Bonus "Spiritual Fortitude" note Negate Spirit Point, stat and Will decrease and can still perform any action, you're screwed. Second, due to most of your allied units' having a size rating from SS- to M- (with just a few being L-sized), Kali Yuga towers with a size of 3L, which means dealing additional damage while receiving less in return. Combined with a list of pilot skills such as a max level "Prevail" note The lower the HP, the greater the increase to accuracy/evasion/critical/armor stats, "Guard" note At 130 Will, -20% to damage received and "Counter" note Chance of attacking first before the enemy strikes first, alongside high armor and stats for everything, even if you fully commit Spirit Commands against her, without a high enough evasion rate, she can attack first via Counter and reduce your attackers' stats by half, rendering their attacks next to useless. The catch of the fight is that you have to fight another boss unit beforehand (which is no cakewalk, either) and you have to deal 30% damage to Kali Yuga in order to trigger the recovery event. Of course, no SRW boss is unbeatable, but due to the gameplay structure of UX (no equippable parts and fewer Spirit Points for sub-pilots), even Gaiou appears easier.
The potential exists to flip the odds as like Super Robot Wars K, there's no pilot skill slot limitations, just a matter of how many "Skill Parts" you have. With enough playthroughs, you can turn a single unit into a One-Man Army.
That One Level: Although scenarios in UX are generally more forgiving than L, it has quite a crazy amount, especially late-game.
The most well-known, but unexpected example happens on Scenario 23, "The False Songstress". This is your usual "defend a certain area" scenario (except half of the terrain is water) and it's mostly easy, until Ranka Lee is captured by a Hound Vajra, adding the objective "reduce the Hound Vajra's HP to 10%". First off, it only has slightly better stats than other Vajra (it's one of the late-game mooks), so accidents do happen if one doesn't check its HP first (for example, Jin Hagane, the writer of Demonbane, had personally kicked Ranka to hell via an Atlantis Strike). Second, if you accidentally summon Tobikage to the field, due to its AI patterns, it'll directly go for that Hound Vajira and achieve a One-Hit KO. Third, even if you don't summon the Tobikage, Brera Stern, who is supposed to help you as an NPC, will do the same thing to Ranka if you don't act fast enough. This scenario is so frustrating it has created numerous new memes, like "Killing Ranka without mercy", "Victory Condition Thief" for Tobikagenote In addition to its infamy of stealing your credits, experience and conditions to unlock secrets, and "Ranka Slayer" for Tobikage and Brera.
Except Brera can't deal enough damage in one hit, and the Hound Vajra has a defensive barrier. Even if you leave it to Brera, he will lower the Hound Vajra's HP below 10% himself with the pattern he uses. Still, two problems remain: Brera's strongest attack is capable of destroying the Hound Vajra in two hits, and because Brera comes with boss-like stats, the Hound Vajira will also target him (again due to the AI) if he's in range, thus the situation isn't much better. Let's not take into account for chances of landing critical hits...
Scenario 46 "The Beautiful Dystopia": succeeding to land the Pretender on the designated area is a challenge itself, and after your reinforcements arrive and destroy some of the mass-produced Machinas, the Deus ex Machina arrives and reduces all your allies' Will by 30 (except Kaidou and Magami, where they either gain +30 Will, lose 20 or are unaffected). At this point, if you don't act fast enough, your units and battleships will be surrounded and destroyed due to the enemies' Will bonus. Deus ex Machina also moves twice, has the "Over Ride" unit ability note At 130+ Will, gain the effects of "High Speed Evasion". The activation rate is determined by the pilot's skill stat, with the "Special Evasion" rate reaching 40% at max. Does not cost EN, and all terrain during movement is ignored, a MAP weapon and HP/EN regeneration.
Scenario 47 "Heaven and Earth": 70% of the map consists of water, which limits your options to air-based units and any units with a decent sea terrain adapability. This makes the red Festum much harder to deal via Demonic Spiders and, in the case of not having enough units adaptable at sea, a terrain bonus. If you want to save Misao Kurusu, all Fafner units must deploy, and each must fight him once, but only a few of them can deal with such a situation. Oh, and the reliable Kazuki and his Mark Sein? He won't show up until you lower Kurusu's HP enough.
In Scenario 48, the last of the ELS appear. Recall their entry in Demonic Spiders, and this scenario features lots of them, and they come without limits. You think the ELS are your only problem? Zerokage also pops up with his force, enough to distract you, alongside a few big ELS partner units around the designated area after Setsuna arrives. In the meantime, you have to be cautious that a random ELS may race down to the southern edge of the map, or gangs of ELS may suck up all the EN from one of your battleships, while you have five turns to send Setsuna to the designated point. Talk about a race against time and a war of attrition.
Tier-Induced Scrappy: Some "Full Upgrade Bonuses" and "Ace Bonuses" for mecha and characters, respectively, are quite weird in UX.
Kenji Kondou's Mark Nacht gains EN +150 as a Full Upgrade Bonus, except it primarily uses ammo-based weapons, whereas Mamoru Koudate's Mark Funf gets EN +50 and its attacks uses EN for a lot of things, such as a Combination Attack that costs a plenty of EN. Naturally, you can see why it should be swapped around. Also, Kazuki's Level 3 "Assimilation" ability note When hit with an enemy attack, decrease enemy pilot's Will; when attacked and Will goes below a certain threshold, enemy will be absorbed and destroyed. Recover HP/EN; the effect increases the higher the pilot's Will in the Mark Sein can only be used against enemy Festum. While he could use it to assimilate AI-controlled enemy mooks such as Shamans and Banks from Tobikage, Kazuki doesn't want to assimilate humans, ELS and Vajra; the same applies to Kurusu if you manage to recruit him, though by that time, there are no longer any Festum to assimilate.
Certain characters like Miu have questionable Spirit Command sets: for her, she has "Strike" note Gain perfect accuracy for one turn, "Alert" note Successfully evade the next attack, "Accelerate" note Increase pilot's movement range by three upon movement, "Justice" note Reduce EN, Magic Points, and ammo costs to zero for one turn, and "Love" note Gain the effects of the Accelerate, Strike, Alert, Valor, Spirit, Gain and Luck Spirit Commands for one turn, yet the latter has the effects of the first three. Her Painkiller has EN+ as a Full Upgrade Bonus, even though "Justice" can render EN costs moot, as well as the Painkiller's "Super Full Upgrade Bonus" via achieving an Ace/Super Ace status of Mobility +5, which is basically useless since she has "Alert". Finally, the Painkiller only has small HP regeneration compared to the Hind Kind and Deceive. This could be a very strong case of Nerf.
Setsuna's 00 Qan[T] uses EN for all of its attacks and the EN costs are no joke. Sure it has 25% EN regeneration, but that's not enough, and is most noticeable during the Downloadable Content campaign scenarios where you have no upgrades. Lockon's Zabanya (and Zabanya Full Equip) also uses EN for the majority of its stronger attacks. While he was originally a sniper, this is probably expected, but he does not learn "Justice", so you can't really use him much. However, Setsuna and Lockon are still considered the ones in the higher end of the tier list.
As a footnote though, the design philosophy of the partner systems in UX (and by extension, L) is to urge players to use usually-unused units in their teams, as less powerful units will have a better bonus, not to mention that drain EN from weapons is increased by a sheer amount since L to discourage a One-Man Army.