The Ancient Forest in Monster Hunter World is the first open area the player will venture through in their long quest. While most of the monsters in the Ancient Forest are pretty easy to take down, there are a few notable exceptions. In the base game, there are 10 possible Large Monsters to encounter in the Ancient forest, not counting Elder Dragons or monsters added in the Iceborne expansion.
The Anjanath, a firey Tyrannosaurus Rex-like large monster that patrols the zone, is initially one of the most fearsome monsters the player will face. As the game goes on, though, the Ancient Forest starts to harbor dangerous large monsters that even the Anjanath has no chance of taking down.
9 Great Jagras
The Great Jagras is one of the first monsters in the Ancient Forest that the hunter is tasked with killing. It seems impressive enough in its introductory cutscene when it consumes one of the many Aptonoth small monsters of the region, but unless you're fighting a high-rank version of the Great Jagras, it's a piece of cake.
The monster's low health pool, as well as its slow movements and easily dodged attacks, make it a walk in the park for any Hunter who knows their way around the basic controls.
8 Kulu-Ya-Ku
The Kulu-Ya-Ku is a large monster that appears in both the Ancient Forest and the Wildspire Waste. It's an egg-stealing Dodo-like creature that pecks and tramples enemies in its path. It's not normally hostile, and will only engage if threatened or attacked.
It's the most annoying monster to show up during an Egg-related quest, as it will find you and steal your egg. It's got low health, and should be easy enough to slay if you can get out of the way of its rapid pecking attacks.
7 Pukei-Pukei
The Pukei-Pukei is one of the first major challenges a hunter will face in Monster Hunter World. The Pukei-Pukei has poisonous attacks and a far-reaching poisonous tongue, as well as fast attacks and evasive maneuvers in its skillset.
The Pukei-Pukei's skin is tough and many parts can cause a weapon to bounce off rather than connect. However, its head and tongue are very susceptible to damage. It's best to attack its tongue when it lashes out, as eventually it can be severed which limits its poison abilities.
6 Tobi-Kadachi
The Tobi-Kadachi is one of the most well-named monsters in Monster Hunter, and in Monster Hunter World it's one of the first large monsters that the hunter encounters with lightning abilities. It can stun the hunter as well as cause Thunderblight, which increases the chance of being stunned.
The Tobi-Kadachi moves fast, has a gigantic tail which it will use in some attacks, and flies above the player, making melee attacks slightly less useful. It's weak to Poison damage, though, which can be imbued into gear with a few kills of the Pukei-Pukei.
5 Anjanath
The Anjanath is one of the most iconic enemies of the Monster Hunter franchise. Taking the appearance of a Tyrannosaurus Rex with a furry mane and fiery breath, the Anjanath is as fearsome in a fight as it is in appearance.
It has a huge health pool, a mix of rapid attacks and brutally destructive attacks (including a one-shot fire breath ability) but the fact that the player can roll out of being on fire makes it a more manageable fight than some of the more unforgiving monsters of the area.
4 Rathian
The Rathian is the female equivalent to the Rathalos, and the two act as partners whenever they both show up on the map. The Rathian by itself, though, is a little bit weaker than the Rathalos although they both have similar move sets.
When fighting a Rathian, listen carefully for distant roars. If you hear one, get out of there immediately or equip a Gilly Suit, because it means a Rathalos is on the way to aid its mate.
3 ... and Rathalos
The Rathalos is the male equivalent of the Rathian, and serves as a figurehead monster of the Monster Hunter series. It's instantly recognizable for its beak-like black nose, but don't spend too long admiring its terrifying beauty or you might turn into its next meal.
The Rathalos and Rathian are nigh on impossible to take down if they fight together, rivaling even some Elder Dragon fights later in the game. Alone, though, each of these wyverns can be taken down with a mix of patience and seeking the right opportunities to strike (which are few and far between).
2 Bazelgeuse
The Bazelgeuse is a large monster that technically first appears in the Wildspire Waste area, but shows up in the Ancient Forest later in the game. The Bazelgeuse is an even larger, even more brutally difficult wyvern than the Rathalos, and it's got an absolutely massive health pool to boost.
It announces itself by firing a series of explosive projectiles from its wings above its target, which usually blow them apart in seconds. It can also inflict Fireblight, which slowly burns away the victim's health and prevents any regenerative effects. Attacking the Bazelgeuse's weak head and the severable tail is the quickest way to down this fearsome foe.
1 Deviljho
The Devilijho is arguably the most dangerous monster players can find in the Ancient Forest (without installing the Iceborne expansion). It was added shortly after Monster Hunter World's initial release, and while it's not particularly dangerous on its own with a middle-of-the-road health reserve, it is almost never fought in a one-on-one situation.
The Devilijho will randomly invade high-level quests (marked with a six-or-seven-star difficulty), or while the Hunter is currently engaged with another large monster. It will attack literally anything it can, start a turf war with Bazelgeuse and Rathalos, and will consume large monsters when defeating them – it is so powerful that it will use other wyverns as weapons as it throws their bodies around. It's terrifying to witness, but as long as the hunter stays out of its way it will actually whittle down the health of other large monsters in the area.