Crystal Orb Spider

Pack Tactics. Crystal orb spiders gain advantage on attack if an ally is within 5 ft. of it, and not unconscious.

Omni-walk. Crystal Orb spiders can freely move on any surface without penalty.  Being able to walk on walls, ceilings, and magically slick surfaces without needing to make an ability check. 

Blood Swarmer. Crystal orb spiders gain +1 to hit for any, and all allies currently engaged in combat, up to +5.  Deals +1 damage to each consecutive hit against the same target.

 Challenge Up. (DM Notes) Monsters can scale between 1/2 to 2 CR at your Discretion.  Combo magic is at higher CR's, and for specific encounters you are free to start off in a specific state.  Higher CR version gain double health per CR increase, up to at CR2 having 4x normal hp.  Starts with two usually, however can use up to six per starting encounter.

Bounce. As a bonus action, can leap to anywhere within 30 without causing an AoO if used to disengage from combat.

Rapid Strike. Melee Weapon Attack: +2 to hit, reach 5ft., 1 target. Hit: 5 (1d8 + 1) Slashing damage.

Stabbing Strike. Melee Weapon Attack: +2 to hit, reach 5 ft., 1 target. Hit: 15 (2d8 + 3) [Piercing] damage. Target must make a STR save against grappling, if failed target is impaled, and must spend the next action attempting to remove two steel claws from themselves, or have assistance from a nearby ally.

Reaping Spiral. Ranged Weapon Attack: +2 to hit, range 5/30 ft., # target. Hit: 14 (3d6 + 2) [Bludgeoning + Slashing] damage.  The spider rears up before launching itself towards a target direction up to 30 ft., covering a 10 foot diameter area with whirling claws.  If hit, target must make a DEX save to avoid being knocked prone, equivalent to, or higher than damage dealt. 

Pounce. Ranged Weapon Attack: +2 to hit, Range 5/30 ft., 1 target. Hit: 15 (3d6 + 3) [Bludgeoning + Piercing] damage.  Leaps to target.  Target must make a DEX save to avoid being knocked prone equivalent to, or higher than damage dealt.  Success, or if attack misses displaces target back 5 ft.

Multiattack. Orb spider makes 2 rapid strikes against a target followed by a stabbing strike.  OR on a successful hit on Pounce/Reaping Spiral, gains one additional action once per turn.

Elemental Absorption. Upon being struck by an elemental spell; orb color changes, and the construct gains special properties based upon element used.  Counter spells, or opposite elements can dispel currently absorbed magic, or overpower in terms of a critical roll.
Absorbed Fire. Construct slags slightly, orb turning red.  Deals 1d4 fire damage on hit with chance to ignite target.  Opposite: Ice, and Water.
Absorbed Lightning. Construct is overcharged with power; turning the orb a bright yellow, gaining +5 Initiative, and double DEX based saving throws.  Able to attack once as a bonus action. Opposite: Earth
Absorbed Cold. Construct is slowed partially as ice forms on the limbs of the construct as the orb slowly changes into a light blue, increasing AC by +2, increasing striking range by 5 ft., however at the expense of reduced -2 DEX saving throws.  Opposite: Fire
Absorbed Earth. Construct is strengthed by the ground it stands upon; turning the orb green.  Melee attacks create minor shock waves that explode from the ground upon striking. Shockwave is 1d8 force damage deal to target square, and the square behind it.  Target must make a CON save to resist being knocked back, and the square behind it must make a DEX save to avoid the blast all-together.  Opposite: Lightning, and Wind
Absorbed Water. Construct relaxes as the orb turns a deep cerulean blue, gaining double to saving throws, and attacks against it are at disadvantage.  Opposite: Fire, and Ice
Absorbed Wind. Construct shifts to a quicker stance, attacking rapidly at the cost of damage.  Orb shifts to a light grey color, and able to multi-attack at half damage.  Opposite: Earth, and Lightning.

(Bold opposites have unique effects if applied after original element, otherwise it has no extra effect.)

Combo Earth & Wind. A unique blend of magics causes the orb to turn a sandy brown, and create dust storms to block vision, on top of half effect from both base elements.
Combo Water & Ice. A unique blend of magic causes a sheath of ice to form over the entire construct.  Hampering movements, however increasing the raw power of the construct.  Speed is reduced by half, and DEX saves modifiers are halved as well.  On melee hits, eruptions of ice shards similar to the Earth element absorption strike for cold damage.
Combo Wind & Lightning. A unique blend of magic cause the orb to flicker yellow as it reaches over the normal threshold for contained power.  Movement is doubled, and gain +2 to hit, and +5 to initiative.  However max health is reduced by half, and vulnerable to being displaced.  Can have a one use Lightning bolt spell to discharge at a target to return to a lower power state.

Shatter. If the crystal orb is damage by force damage, or by sufficient amount of physical damage, it will shatter, causing the construct to disintegrate.  IF applicable for circumstances, another spider will spawn to take it's place.