Acromantulas

The Acromantula is a gargantuan, eight-eyed spider capable of human speech. It originated in Borneo, where it inhabits dense jungle. It has thick, black hair that covers its body, a legspan that reaches up to 15 feet, and poisonous pincers, which produce a disntinctive clicking sound when it is excited or angry.

The Acromantula is carnivorous and prefers large prey. It spins dome-shaped webs upon the ground. The female is bigger than the male and may lay up to one hundred eggs at a time. Soft and white, these are as large as beach balls. The young hatch in six to eight weeks. 

The beast is believed to be Wizard-bred, possible intended to guard wizard dwellings or treasure. In this case it differs from the typical Dark Creature one usually encounters. Depsite its near human intelligence, the Acromantula is untrainable and highly dangerous to Wizard and Muggle alike. Acromantulas fear Basilisks more than anything.

 Basilisks

The first recorded Basilisk was bred by Herpo the Foul, a Greek Dark Wizard and Parselmouth, who discovered that a chicken egg hatched beneath a toad would produce a gigantic serpent possessed of extraordinarily dangerous powers.

The Basilisk is a brilliant green serpent that may reach up to 50 feet in length. The male has a scarlet plume upon its head. It has venomous fangs, but its most dangerous means of attack is the gaze of its large yellow eyes. Anyone looking directly into these will suffer instant death.

If sufficiently fed, the Basilisk may live to be very old. It will feed on all mammals, birds, and most reptiles. Like most snakes, it will shed its skin periodically. The creation of Basilisks has been illegal since medieval times, although the practice is easily concealed by simply removing the chicken egg from beneath the toad when the authorities arrive.

Basilsks are uncontrollable except by Parselmouths. They are dangerous to everyone, including most Dark Wizards, although the legendary Griffin and the Phoenix both seem immune to the Basilisk's powers.

The tough exterior skin of the Basilisk proves to be immune to simple magical spells like Stunning Spells. The only vulnerable areas on a Basilisk are its eyes and the roof of its mouth.

How to defeat  these creatures

Acromantula

The best spell to use against the Acromantula is Arania Exumai this spell knocks the spider down on it's back, or in an attackable position.  I find that a Blasting Curse works nicely, but if it is a particularly nasty encounter, I will not hesitate to use Diffindo or Sectumsempra, both which will cut the Beast into a bloody pulp. I've also been known to use the Entrail Expelling Curse, which does, exactly what it sounds like it does...the result is instant death.

Basilisk

The Basilisk is a little trickier, because you can not look into its eyes while fighting it. And, because of its incredibly thick hide, you must aim for the vulnerable areas. I find the Conjunctivitis Curse quite effective. This will blind the Basilisk while you then cut, either magically, or physically its eyes out. If you are extremely proficient, you might attempt the Engorgio Curse....BUT ONLY AIMED AT THE ROOF OF THE MOUTH!!!! Anywhere else would be disaster, but when aimed properly, the mouth will engorge and suffocate the Basilisk.