For the vast majority of game, immunities are cut and dry. If a champion's description states that they are immune to an effect, then that effect cannot apply to them under any circumstance. Hulkling is immune to shock, therefore no shock effect (debuff/passive/instant) can apply to him. Valkyrie can be immune to stun debuffs, making them incapable of applying, but stun passives can still render her incapacitated. Omega Red is immune to poison and resistant to bleed which means that while poisons cannot apply to him, bleed effects still can but have 100% decreased potency. Immunities to effects such as these have worked in this way for as long as I can remember as a 9-year veteran of this game. Even immunities to attributes such as regeneration rate follow this rule. The description of Wolverine (Weapon X) states, "Immune to All types of Regeneration Rate Modification except due to poison." If you attempt to apply an effect that modifies regen rate such as petrify or spectre, the effect simply won't apply. With Hulk (Immortal) and Lady Deathstrike, whose abilities state that their regen rates cannot be altered but do not state that they are immune, such affects still apply to them, but they do not modify their regen rates. This all seems very intuitive; immune means the effect cannot apply while "cannot be modified" or similar wording means that the effect applies but doesn't work.
The only exception to this seemingly unbending law of the contest is in the case of Ability Accuracy. But before we get into that, I need to explain why all of this matters.
When Tigra entered the contest in June of 2020, she also introduced a brand new game mechanic: neutralize, an effect that reduces buff ability accuracy by 100%. And boy did it not work as intended! Neutralize would not only apply against champs and nodes with a stated immunity to AAR, but it would work too. Nodes like Force of Will and champs like Mordo had buffs completely shut down by Tigra. This obviously had to be fixed, but the patch to this bug took two years to finally happen, during which time players had just accepted this new reality of the game. When neutralize was added to the list of effects that AAR immunities countered, there was some controversy, but it was of my personal opinion that no matter how much I loved Tigra's ability to bypass such immunities, she was breaking the fundamental rules of the game. This change would hurt her much more than any other neutralize champ since not only her utility but her damage was drastically affected without being able to apply neutralize and pause her senses, but I assumed that this would only nerf her in a very select number of matches. For the most part, she would still be the same champ I loved, right? Much to my disappointment, I was wrong. The Force of Will node seems to have appeared much more frequently in the game, especially in Battlegrounds. Every other season I've had to bench my favorite and most heavily invested-in champion as she was rendered utterly useless in the face of Ability Accuracy Reduction Immunity. The surprise addition of Force of Will into the most recent BGs meta just 24 hours after it began sparked me to investigate exactly how AAR immunity works.
There are many effects in the contest that modify ability accuracy. Some such as Magnetism, Danger Sense, and Neurotoxin have multiple effects and therefore "bypass" an immunity to AAR; these effects still apply and their other abilities still work, but the AAR portion does not affect the champ with the immunity. Only 3 effects to my knowledge singularly modify ability accuracy: Neutralize, Tranquilize, and Concussion (technically Falcon's Lock-On should too but while it's active his attack rating for basics is increased so I didn't include that in my research). I decided to test these 3 effects against champs and nodes with AAR Immunity, and the results I found were incredibly confusing.
For starters, of the 6 champions in the game that the majority of the player base understands to have AAR immunity against all champions, only 2 of them have descriptions that explicitly state that they are immune. The other 4 have the previously mentioned "cannot be altered" statements. I've compiled my findings into a chart below:

Note: I haven't ever uploaded a photo on this forum site so I have no idea if it will load. I'll include the link to the spreadsheet here:
https://docs.google.com/spreadsheets/d/1bZH3sgA8ErJZnZQQsU4IWYXGajXM_OHhm7uBcxFzEcI/edit?usp=sharingIn contradiction to everything we thought we knew about immunities and how they should work, AAR Immunity is wildly inconsistent. Champs such as Mordo and Mephisto who should be immune to Neutralize and Tranquilize can still have these passive effects applied. Then champs that are not immune but simply cannot have their ability accuracy altered in one way or another -- such as Archangel and Mysterio -- are operating as if they are immune to the application of Neutralize and Tranquilize which should not be the case. The inherent laws of the game are being broken by these interactions, and they need to be fixed by Kabam. There are three solutions to this pressing issue that I would like to pitch and discuss.
Solution #1: Fix the Descriptions
This one is the simplest change in theory and in practice. If the contradictory descriptions of these champions were made to reflect what actually happens in game, then the majority of the confusion would be cleared up. Altering an ability description is, I'd assume, very easy to do from a developer perspective and does not change any game mechanics that the player base currently knows. If Mysterio was stated to be immune to AAR then the interactions reflected in game would make sense.
Solution #2: Fix the Interactions
This change involves a bit more work on the part of Kabam with a similar end result as the first solution. The ability of the champ would be changed to fit the description. Mordo and Mephisto would be Immune to AAR effects, and such effects would be incapable of applying to them. Archangel, Old Man Logan, and Mysterio could have these affects applied, but they would not work to alter ability accuracy. I haven't mentioned Shuri or Force of Will in either solution because their descriptions already match their interactions. Both solution #1 and #2 solve the immediate problem, but I believe there is one more way to resolve this issue in the most player-friendly way possible.
Solution #3: Remove the "Immunity" Statement from AAR Immune Champs and Nodes
This is the most radical of the solutions but the only one that solves a major injustice -- a mechanic in the game that affects one champion unequally when compared to all others: Tigra. As I stated before, there are many champions who are affected by AAR Immunity. Some lose a major piece of utility, some miss out on damage potential in combination with other abilities and nodes (i.e. Force of Will paired with Safeguard has a much greater impact on Falcon's damage potential than with Force of Will alone). However, Tigra is the only champ in the entire game whose damage potential is completely turned off in every single matchup with AAR Immunity. Now, I know what some of you reading this post (if anyone gets this far) are thinking. Plenty of champs have "kill switch" nodes, like Ghost with Armor Break nodes, Quake with True-type nodes, and Magik with Power Manipulation Immunity nodes. The difference is that these champions are insanely broken, with Quake and Magik deemed so dangerous to the balance of the game that they may never be introduced at a higher rarity level. Tigra is not at their level. Additionally, these nodes take away the utility AND damage of multiple champs. AAR Immunity takes away the damage of only Tigra. She is not deserving of a "kill switch" that is found so often in so many game modes in the form of Force of Will. The best way to remedy this completely lop-sided affair is to stop treating AAR as something that one can be immune to and instead let it only be an attribute that some champs and nodes can not have modified.
I'm asking Kabam and the players of MCOC to truly consider this plea, at least in some way, shape, or form. At the very least, the current system of AAR Immunity is flawed and desperately needs a tune up. AAR Immunity breaks the laws of the game and must be fixed.