Malmalam Thicket is quite a peculiar "dungeon", as the whole area is located above ground, in a thick forest. Additionally, this is a very linear location - there are no side paths and locked passages here and you will be traveling along the only available path throughout the whole dungeon. The recommended level to visit this area is 35. At the end of the dungeon you will be facing a boss, Bandersnatch, protecting a Royal Tomb with the Scepter of the Pious hidden inside.
Malmalam Thicket is located in the south-western part of the map. You can use Regalia to get there. Head west from Old Lestallum and park the car near Maidenwater. Now you have to travel through the forest to reach the entrance to the dungeon. The location of the entrance to the dungeon can be seen on the above screenshot.
Vulnerable to Swords, Firearms and Fire, resistant to Lightning and Light. Inflicts Mollified (reduces Strength) and Confused statuses.
Vulnerable to Polearms, Daggers and Fire, resistant to Lightning and Light. A flying enemy. Inflicts Confused status.
Vulnerable to Polearms, Firearms and Ice, resistant to Fire and Light.
Vulnerable to Light, resistant to Swords, Greatswords, Polearms, Daggers, Firearms, Shields and Machinery.
Vulnerable to Polearms, Machinery and Lightning, resistant to Fire and Light.
The enemies you can find in this area are resistant to Light, which is why there's no point in using weapons with that parameter. The most versatile are Firearms, as two enemies are vulnerable to those weapons and, above all, Polearms - all types of spears will be effective against enemies fought in this dungeon.
Run through a narrow passage located at the end of the road to reach Malmalam Thicket. The location should be visited during the day, as during the night the visibility is poor and you can easily miss some of the items here. Right after you enter the place you will stumble upon your first enemy - Mandrake. The enemy isn't that strong, but it can inflict two negative statuses. The first one, Mollified, decreases the Strength attribute of a character, whereas the second one is "Confused". With the latter your controls will be reversed and your companions will sometimes miss their attacks, slashing through the air. The enemy is quite slow - you shouldn't have problems taking it out before it can inflict the mentioned statues.
Once you're done, continue your march and you should soon run into another encounter, this time with two Mandrakes. Focus your attention on a single foe to take it out as quickly as possible and try to dodge/counter all of their attacks to minimalize the chances of them causing the effects described in the previous paragraph. Afterwards, collect the item - Thunderbolt - lying nearby. This is a powerful lightning-infused Greatsword, capable of dealing huge damage to enemies weak to that element. This weapon will be useful against the boss in this area, Bandersnatch, who is vulnerable to Lightning.
Continue the march along the route and you should soon encounter another enemy - Soldier Wasp. Those oversized wasps, similarly to Mandrakes, are capable of causing the irritating "Confused" effect and, to make matters worse, they can fly. However, those foes are more irritating than dangerous, as they are incapable of dealing any real damage. Take the bug out, collect Malmashrooms growing to the west of your current position and continue marching south, where another encounter, this time with a trio of Soldier Wasps, await you.
You should soon encounter a pair of new enemies - Shieldshears and Flan. Don't be fooled by their low levels - Shieldshears can hit really hard, taking out more than 1/3 of your character's health with a single strike and Flans are resistant to almost everything aside from Light, from which it receives slightly increased damage. The enemies can be taken out with an Ice spell - Shieldshears are vulnerable to that element and Flans have low health pools. Additionally, the enemies are located in a narrow passage, which should allow you to easily take them out with a single spell.
You should reach a place where you will be able to set up a camp. You should use this opportunity, especially if the enemies damaged your party. Afterwards, jump down to water and head upstream (north), where probably the most difficult encounter awaits you. You will be fighting with two Shieldshears, two Mandrakes and a single Soldier Wasp. Start off by taking out Mandrakes, then eliminate the Soldier Wasp and leave the crab for the end, as this foe is rather slow and shouldn't pose any real threat.
Afterwards, head west towards a small waterfall. Here you have to climb up, turn right (north) and head along the narrow path. You will soon reach an open area where the final encounter of this dungeon takes place. You will be fighting Bandersnatch. The enemy looks dangerous but the battle is not that difficult. The perfect weapon to use against the beast is the Thunderbolt Greatsword you've collected at the beginning of Malmalam Thicket - the enemy is vulnerable to Lightning and the weapon is infused with that element. The encounter can be made even easier by using a simple trick. Attack the legs of the beast - after several strikes the enemy will fall to the ground and enter the "Vulnerable" state, giving you several seconds to deal increased damage to it. Once you've defeated the enemy, head inside the nearby Royal Tomb to collect the Scepter of the Pious. The location is now clear and you can leave this dungeon.