Basic Trope: A character/ability/item that starts out powerful, but becomes less useful as the game goes on.
Straight: At the beginning of the game, Bob is your strongest character, but your other characters start overpowering him later in the game.
Exaggerated: Bob is all but a Game Breaker... For all of the first dungeon. After that, he only hits enemies for 1 damage and dies in one hit.
Downplayed: Bob can still slog through the rest of the game, but for maximum effectiveness it's best to switch to another character.
Bob is a grizzled old fighter who can defeat weaker enemies with ease, but can't catch up with the newer fighting styles that the other characters and tougher enemies use.
In an RPG, Bob is a latecomer to the group, and in order to avoid a large imbalance between his level and the others (so that he is not ignored by all who play), he has an item which gives him a nice power boost. This boost is proportional to the difference between his level and the others, so that he is not useless at first but the item becomes less and less powerful as Bob catches up.
Bob is actually hiding his true strength. In the first dungeon he easily defeats enemies because he uses just enough abilities to get over the weak enemies, but declines to show his true strength for some reason. He keeps acting weak after because he fears being caught more than holding back and having the party fail.
Bob was an anti-slime warrior for the local village, and the first dungeon is full of slimes. After the first dungeon, Bob's specialization means that, after the first dungeon, his talents don't work as well, and he only follows the heroes because he counts as a knight, and he is aware of his specialization impacting his abilities.
It would seem that Bob is getting less powerful, but he's still one of your better characters later in the game.
Bob is superficially strong, but turns out to be more difficult to use well than first apparent.
Double Subverted: He turns out to be completely underpowered at the final dungeon, though.
Bob is a Jerk Ass who is deliberately not giving 100% so he can enjoy watching Alice and Report Siht attempt to not die.
Alternately: Bob's class is "Goblin Slayer," and all of his skills and bonuses are focused on killing goblins, disarming goblin-made traps, and so forth. You kill the last goblin in the entire world in the second dungeon.
Zig Zagged: Bob's usefulness fluctuates wildly throughout the game.
Averted: No character starts out significantly stronger than the others early on.
"The game testers said the game is way too hard in the beginning. Let's give players a powerful character to start with to make it easier".
Lampshaded: "Bob is a strong guy, but don't rely on his power too much; if the others don't get some fighting experience, you'll be in trouble later on".
Invoked: Bob purposely lets the others get stronger than he is so he can retire.
Defied: To avoid being left behind, Bob continues to train himself to remain one of the strongest in the party.
Discussed: "You know, Bob, if you don't keep up with your training, we're all going to become more powerful than you later on!"
Conversed: "Don't use Bob".
Possibly due to EXP Wutai Theft, Bob becomes a character that no serious player would use, to the point where players wonder why he's even in the game.
Bob becomes aware as the story progresses that the rookies he used to look out for are outpacing him and he Can't Catch Up. Despair and/or jealousy overwhelm him, getting worse as the gap between them widen...
Bob is still recognized as "a good character for beginners to use" to adjust to an otherwise-difficult early learning curve.
Instead of getting frustrated, Bob takes pride in watching the former rookies blossom and grow more powerful, and eventually retires after becoming certain that they won't need him holding their hands and protecting them any longer.
Bob even offers to train his eventual replacement, Charlie, so that his experience doesn't go to waste.
Back to Crutch Character. It's not a very good page the further down you get, though...