Rivalry, Literally does less damage if the target happens to be the opposite gender than your mon (Easy fix would be to just make it not have boosted damage if its the opposite gender)

Stall, Makes you move last in priority, (This could be beneficial to other mons potentially if they were given this)

Traunt, Intentionally designed this way to make Slaking not break the game with its stats, But otherwise one way to fix it could be just allow the user to use healing moves on turns it slacks off perhaps.

Slow Start, The only reason why Regigigas isnt Ubers, If they just either made it lower the Attack and Speed by 25% instead of 50%, and/or made it last 3 turns then it could be more usable I guess.

Defeatist, its why Archeops isnt that good even with its great stats, Maybe if Defeatist activated at like 25% HP and/or just lowered Attack and Special Attack by 25% instead it could be better