Spider Climb. The spider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Web Sense. While in contact with a web, the spider knows the exact location of any other creature in contact with the same web.

Web Walker. The spider ignores movement restrictions caused by webbing.

Magically Independent. The Arcano Spider seems to draw power from a wild and unpredictable source, as such for better or worse, the Arcano Spider is immune to any abilities that would force it to re-roll or bypass rolls for its attacks, ability checks, and saving throws. (this does not effect bonuses after the roll like Bane or Bless)

Infusable. If the rider who is attuned to the Arcano Spider casts a spell into it, the spider can attempt to channel that magic into itself.  When a first level or higher spell is cast targeting the spider, it must succeed on a DC 10 Wisdom saving throw (-1 to the save DC for each level above 1st). On a success, the spider gains 1d4 per the spell's level of additional damage on each of its bite attacks for the next minute.  the type of damage is determined by the DM based on the spell cast into it.  If the spider fails the saving throw, it instead takes 1d4 per spell level of force damage) 

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 7 (1d8 + 3) piercing damage, and the target must make a DC 11 Constitution saving throw, taking 9 (2d8) poison damage on a failed save, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way. If the Arcano Spider rolls a natural 20 on a bite attack, it may roll on the Arcane Spray table for an additional effect on the target.  If the Arcano Spider rolls a natural 1, it explodes in a 10ft radius sphere, dealing no damage to itself, but forcing every creature within its range to make a save against a rolled Arcane Spray effect. 

Arcane Spray (Recharge 6). The spider produces a swirling 15ft cone of arcane energy. Each creature in that cone must make a DC 12 Dexterity saving throw, taking 12 (6d4) Random Magic damage on a failed save, or half as much damage on a successful one. The Random Magic damage type is determined by rolling a d8 with the following effects being results:

1. Red. The target heals for 6d4 damage instantly regardless of its save
2. Orange. The target takes 6d4 acid damage on a failed save, or half as much damage on a successful one.
3. Yellow. The target takes 6d4 lightning damage on a failed save, or half as much damage on a successful one.
4. Green. The target takes 6d4 poison damage on a failed save, or half as much damage on a successful one.
5. Blue. The target takes 6d4 cold damage on a failed save, or half as much damage on a successful one.
6. Indigo. The target takes 6d4 psychic damage and can be teleported to a point of the spider's choosing up to 30 feet away. The location must be a point the spider can see.