4. Elder Dragon - Monster Hunter World: Iceborne
The concept of dangerous first-class monsters and special assignments has been a part of the Monster Hunter series for a very long time. It started with the Elder Dragon Fatalis and his initial appearance in Monster Hunter for PlayStation 2. The Black Dragon was one of the most dangerous creatures in the game's universe, and only select hunters could be called upon to fight him. For good reason, as this colossal lizard boy was seriously no joke.
This tradition of limited-time special monsters has persisted throughout the series to this day, and even Fatalis himself makes a return in the recent Monster Hunter World DLC, Iceborne.
The dragon is part of a special event that you unlock after finishing Iceborne's main campaign. He is the largest and most powerful creature in the game, which is why players shouldn't even think of going after him without reaching at least Master Rank 100. Even then, it might take you a while to kill him as he has an insane amount of health and three different phases, and you only have thirty minutes to complete the assignment!
Compared to him, the final boss, Xeno'jiiva, looks like an oversized gecko with wings.