What if someone brought some modified dices to cheat?
Has it ever happened? Lol

To me, no.
I'm sure someone sometime must've tried.
It would be pretty obvious though, unless you specifically used them only when it was absolutely critical.
Worst we had was one powergamer.

Interestingly enough, there actually is a computer game equivalent to this; in some video games, it is possible to exploit the random number generator (RNG).

This does, for example, make it possible to beat the original Dragon Warrior at level 7 in under an hour. (Without RNG manipulation, it takes well over 5 hours to speedrun the game (longer if you are just playing casually), and you are not realistically going to beat the game before level 17, when you learn the powerful healing spells.)

Another example is when playing a game like a Civilization game by e-mail. Even with a persistent random seed, a player can load, try various actions to see what the random number sequence looks like, reload, and arrange matters so that the good random numbers are used when it is most beneficial.

I've heard of this happening in Battle for Wesnoth, and it is quite possible to do this in Nethack (by changing the system time). It's been done in Pokemon games; while doing it competitively might not be feasible, in many Pokemon games it's possible to manipulate the RNG to get a Pokemon with very good IVs, or to get a shiny Pokemon more easily.

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Yes and no.

There are rigged/weighted dice around that you can buy, they roll in a pretty obvious way though. I have four in my possession from about 25 years ago... for show value. Using them in a game would be infinite sacrilege. No player I know would ever risk that. Once you're branded a cheat, you can give up this hobby altogether.

However, all dice have their natural imbalances – bubbles while they're being cast, slight form irregularities, chips and pips (pips in six sided dice usually create a natural imbalance that for some reason makes them roll slightly more ones). And in some circles I played in, it was considered fair game if hardcore players sought out, rigorously tested and then used dice with those slight imbalances.

Lol it sounds like a luck modifier.
"You have been cursed, use the unlucky dice for 3 days".