Dice rolling mechanic where modifiers have a predictable and consistent effect on difficulty

I am looking for a dice rolling mechanic that makes it such that increasing or decreasing a modifier on the roll has a constant multiplier effect on the probability of the outcome.

Say you have to make a roll for STAT. Such a roll has a probability of success of 50%. Now say you roll with a mod of -1, this roll has a probability of success of 25%. -2 has a probability of 12.5%. -3 is 6.25% and so on, always halving. The other way around it should be the same but for the probability of failure, always being divided by the same factor.

It doesn’t have to be a multiplier of 0.5, in fact I’d much rather it was a multiplier of 0.66-0.75, not such an extreme change. The default unmodded value doesn’t need to be 50% chance of success either, it can be something else.

Is there any kind of dice rolling mechanic I can use to simulate something like this?

Psionic talent modifiers stacks?

If you choose "Unlocked Talent", you choose 5 "psionic talents" (also named 0-level psionic powers) then if you have enough power points to spend, you can activate "Precognition, Greater", then "Inertial Armor", then "Thicken Skin", then "Force field". Each of these add Armor Class modifiers and sometime Saving Throws modifiers, can they stack?

Do negative modifiers change a critical hit? [duplicate]

I want to play a champion fighter and am considering whether or not to get the Great Weapon Master Feat which states:

Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a – 5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.

If I take the -5 to attack roll and roll a critical hit, will that crit still be in effect, or will the -5 counteract that? Also, in the event that I do crit with a -5, would I add the +10 damage before, or after I double damage, like with other modifiers. It doesn’t say that the +10 is a modifier specifically, so I was a bit confused (note: for critical hits, my group usually has house-rule to double the damage and then add modifiers instead of the normal double dice.)

When are Ability Scores (not modifiers) used in D&D 5e?

In D&D, the main ability is a score from 1-30, while the modifiers range from -5 to +10 (score -10/2 round down)

In the Player’s Handbook, it states:

Because ability modifiers affect almost every Attack roll, ability check, and saving throw, ability modifiers come up in play more often than their associated scores.

So when do the scores come up?

D&D 5E Multiclass spell casting and spell modifiers

Question is simply this, I know that you use your spell modifier from the class you gained the spell from. However, for something like Tempest Cleric gaining the use of Thunderwave from their subclass, and as a multiclass with Sorcerer who can also use Thunderwave normally (if they want to learn the spell), can I use my Charisma instead of Wisdom as my spell modifier casting Thunderwave with my focus instead of holy symbol?

Do Cantrips Benefit From Spell Attack Modifiers?

While I was rolling to attack for my Warlock’s Eldritch Blast, I said I don’t think it gets my Spell Attack Bonus because I didn’t see it say such anywhere, and the DM (also new to D&D) agreed, said it sounded correct as cantrips don’t get the bonus. As I have been reading however it seems that they do get the bonus to attack rolls, it just certainly doesn’t carry over to damage save rare exceptions. Can anyone verify this to me? And if so, show a source so I could let my DM know?

Extended Vision changes ranged effects modifiers due to distance?

I’m trying to build a character that has an incredible vision, using her Extended Senses (Vision). She uses firearms in battle. I kinda wanted to simulate her efficiency in shooting at great distances at easy, but I got stuck in some rules.

Range attacks have three types of ranges: short, medium and long, each one giving different modifiers base on the distance to hit the target.

A ranged effect has a short range of (rank x 25 feet), a medium range of (rank x 50 feet) and a long range of (rank x 100 feet). Ranged attack checks at medium range suffer a –2 circumstance penalty, while ranged attacks at long range suffer a –5 circumstance penalty.

Extended Vision would be a reasonable choice, but it seems to just affect Perception checks and not range attacks. I could use Extended Distance Extra, but it seems that I would need to apply it to each weapon, or at least for a container of powers. Shouldn’t Extended Vision affect the range for ranged attacks?