Hello, I will be joining a new campaign in the near future and was going to be playing a wizard that would specialize in "Save or Suck" spells but due to my DM disclosing that he fudges rolls this idea does not seem as fun or enjoyable to play. While I understand that many DM's fudge rolls and if done correctly can improve a games health the idea that I can be rendered useless because my DM needs this enemy to not fail my check bums me out, however it also goes into making me question whether or not every time an enemy passes a check is if they did it legit or the roll got fudged. Am I wrong for thinking this way and if so how can I change my perspective?

This is tricky - if the DM is a friend that you trust, you could give them the benefit of the doubt that they will be fudging rolls for selfish purposes (e.g. making their super-duper-awesome boss encounter impervious to all player abilities etc).

If they're not a friend you trust or they are someone you've never played with before, then the mistake the DM has made here is, by admitting he fudges rolls, the Placebo Affect is now in play - as you've mentioned, how can you know for sure the DM is playing fair?

The best solution might be to try a session zero and observe how the DM handles Player Agency and Combat. If you get the feeling that the DM is fudging rolls to take away the impact the players are having on their story or meddling in some other negative way, then just call it quits after the session zero. As the saying goes, no D&D is better than bad D&D.

I would discuss with the DM more details of what rolls he will fudge. At one ond of the scale are DMs who roll in secret purely to protect the party. If in the first combat a goblin wins initiatve, shoots his bow at the Rogue with 10 health and gets a crit they might fudge the damage so they don't immediately go unconcious. At the other end there are DMs who fudge dice to make any save or suck always fail. In between are cases where the spell would be a "We win" card on a failed save, for example Banish only be fudged when fighting a single enemy of a boss with very weak minions.

Once you know you can make your choice

I think the big problem here: Your DM told you about it.  Frankly, that’s a big enough problem that you probably should tell your DM “hey, friendly advice, if you’re going to fudge numbers, please don’t tell folks first.”

There are plenty of good reasons for DMs to fudge numbers. You mentioned saving against debilitating effects, but it also can be the case a DM fudges the number to fail those effects, such as if they’ve legitimately succeeded on a number of them and don’t want the player feeling useless for an entire fight, or the fight is going badly and a save would even the field. 

By telling you, they have now called into question every single roll - even if they only fudge infrequently and only when needed, the perception they might be fudging taints the entire campaign. That was their big mistake - they created a situation where psychology has cast a shadow over the game itself in a way that is nearly impossible to forget.

Now, what can you do to fix it?  You could try to adopt the mindset that your DM is likely not fudging regularly, so the majority of their rolls can be trusted. With enough willpower and mental gymnastics, you can overcome the psychological perception that everything might be tainted.  That is not an easy task (and is much harder when the fudging was specifically stated, rather than implied), but it is possible.

The other option is to talk to your DM about how they have now left this perception on every single roll and explain the only real way to solve that problem is for the DM to commit to straight rolls (they can still roll them hidden, just with the guarantee they will not be fudging).  The DM can compensate by disproportionately running creatures designed to save against certain effects, of running harder monsters. 

As Jegpeg said, it's about what they're fudging.

If they're fudging little things occasionally just to stop a game from getting stale...then they're a good DM and you're fine. They'll probably end up helping you more than harming you, so it's all fine.

If they're railroading the story by forcing every roll to be according to their whim, then yeah, you have a problem. They could end up "succeeding" against all your spells rendering you useless, or they could favour you and end up rendering your progression meaningless. Neither is a good situation. 

You need to chat with them to find out where they are on that spectrum then decide if you're comfortable with their position.

I'm not a fan of fudging rolls generally, especially in 5e: PCs are pretty bulletproof and the DM can give important enemies abilities like lucky, portent, or legendary resistances that let them cheat a little but keep some guardrails up. There are times when it's appropriate though ("Whoops, I wanted the PCs to find this important clue but I set the DC unreasonably high"). 

I'm with most of the others - play it by ear. If you're having a good time and the game feels satisfying to play, stick it in the "don't think about it" box. If you're not, you may want to move on. 

Class and spell selection shouldn't be based wether the DM fudge rolls or not but on what you want to play and cast. If the DM wants to control the outcome of random rolls it's a reality that will certainly have lesser impact if you select spells generating an attack roll rather than a saving throw but if the DM also modify enemies' AC on the fly you won't escape it.

Bottom line is that whatever you play you will always be at the mercy of a fudging DM so you must simply accept it.

Lots and lots of DMs fudge rolls. Lots. Mostly it’s to avoid a tpk if they’ve had a hot streak. Mostly, they are fudged for the the benefit of the PCs. So, I wouldn’t worry about it. 

Frankly, this is why I never fudge a roll. As a DM, the only rolls I don't let players see the result from are rolls with no information the characters would perceive.

i.e. if a Rogue is hiding and a NPC is in a position to possibly see them I made the NPC roll to check, but I don't share the result as a number. I let the NPC communicate it through their action.

Everything else? I roll in public.

My online campaigns all have public rolls as i believe in fairness and transparency when it comes to randomness and prefer to let the dice fall where they may.

In the event that things go sideways in combat for exemple, i prefer to have current enemies retreat inexplicably or new creatures suddenly showing up either as friendly back-up or enemies in a three-way battle that would create diversions than to actually fidge dice. I rely on randomness not to control the outcome.

The cats out of the bag now.

He said he fudges rolls and now you will never trust a roll he makes again.

I have myself and know of many DM's who just roll and make players roll for no real reason. It keeps the players guessing.

I for one would not like it much of the Dm rolled everything out in the open. Player death looms large and fast unless the DM then gives the player every extra chance and then some extras to stay alive.

I also never ever fudge rolls. I tell my players that none of my characters have plot armor. I've had an NPC I planned as a recurring villain get defeated on the very first encounter. That wasn't supposed to happen and it forced me to adapt. But figuring out new solutions is one of my strengths. What I came up with ended up being more interesting than my original plan. A PC was almost killed by the NPC in question but survived thanks to a natural 20 on her third death saving throw after failing two in a row. The PC had received a lingering injury from the attack. After playtesting the rules on injuries, I came to the conclusion that they were way too unfair and debilitating for players. I modified the rules to make them more fair, reducing the odds of getting extremely debilitating injuries and adding new ones. I also made variants based on damage types. For example, the PC received an internal injury from psychic damage, so I flavored it as a form of PTSD that caused her to be paralyzed in fear instead of excruciating pain preventing her from performing an action.

I had already established that injury when the NPC was defeated and captured. There was a whole plotline about slowly getting to know the NPC's motives and backstory each time she's encountered, which was essential as a lead-up to a plot twist at the end of the campaign. Instead, I had to resort to using the psychic injury to my advantage. Even after it was healed, a lingering psychic connection was established between the PC and the NPC. As the story progressed, the PC had dreams about the NPC being interrogated in jail. It's as if the PC was experiencing what the NPC was going through. It's similar to the connection between Harry Potter and Voldemort. It allowed me to expose the important plot points to my players in small doses over the course of the campaign, essentially accomplishing the same goal I originally intended.

In another campaign, the most important NPC is so important that his premature death would completely derail the story. He's so essential that he needs plot armor. But how am I supposed to give him plot armor without giving him plot armor? The solution is simple: he's a cambion. If his life is in danger, he can simply plane shift to safety. It's also mathematically impossible for the players to kill him in a single round before he even has a chance to act. It's also possible for players to choose to never fight him. He's basically a supporting antagonist occasionally showing up to help the PCs or demand they hand over a MacGuffin. He's using the PCs and would rather avoid hurting them, only doing so if they resist. He needs the PCs to succeed in their quest to retrieve the MacGuffins for him. If by some miracle he does end up dying, he has a trustworthy friend who is in possession of one of his body parts, a diamond worth 1,000 gp, and a list of names and locations of people capable of casting the resurrection spell.

My adamant refusal to fudge rolls can also disadvantage the players. Once, I've had a PC die because he received two critical hits in a row from a monster with two attacks. It didn't kill him outright, but he failed his death saving throws. This happened during the first round of the second encounter of the entire campaign. But that's the price to pay when you want the game to be as unpredictable and fair as possible. You never know for sure what's going to happen, and you can be sure that the DM is bound to the same rules as the players.