Part 2, can you give me some hints to make a “still winnable” end game? :D
Randomness versus skill
The more random your game's success is, the less early advantage can project to victory. A drastic example would be a game mechanic that switches places with random players. The other extreme is a game where success is only determined by players´ abilities. So the best player will start winning, continue winning, and end winning. Boring.
You decide how much randomness works in your game. That is no easy task. You don´t want good players to lose regularly because of random events. Nobody likes that.
Catch-Up and Wall-breaker
Catch-Up mechanics support weaker players in reaching the front line. This can be the distribution of speed buffs to the last players in a racing game. This can also be crafting mechanics in an MMORPG where high-level players sell high-level items to low-level players.
Wall-breaker mechanics enforce a higher skill on players that advance from the rest. This can be a slow debuff that only applies to the first player in a racing game. This can be a boss that gets weaker within weeks and months in an MMORPG.
The bomb
There is a type of game where players throw a “bomb” around or pierce swords in a barrel with a pirate. The longer the game goes, the higher the possibility of explosions / the pirate jumping out. This game combines randomness and skill because skilled players will avoid having the bomb or taking action the longer the game goes.
More general, the bomb is an external force whose impact decides or strongly influences the game. The bomb can also be an alien force or the king. Players can work out strategies that put them in favor. So until the end, the game is undecided.
Abort
In a competitive setting, you can have an abort mechanic. The losing player can give up. So you avoid boring games that are already decided.
Cut ahead
In racing, the winning driver can lap other drivers. This effectively puts the winner at the end of the queue again. A similar mechanic is found in some games. When players reach the highest rank, they gain a reward and restart with the lowest rank. So this mechanics brings top players to the bottom of the ladder, making them more interesting.
When you hint at the type of game you have in mind, I can develop more specific solutions.
Best wishes!