Adaptive Arm of the Equestrian

A curious bead that seems to hold power of becoming an adventurer's greatest weapon or worst liability.

You have a +1 bonus to attack and damage rolls made with this magic weapon.

Synergizing Spherule. As a Bonus Action, you choose a common weapon that the bead will transform into for 10 minutes (cannot transform to a firearm except the usual flintlock). All weapons transformed to in this way will have the option to be considered to have the trait finesse. Roll a d100 to determine the additional effects of the weapon.

1: The item explodes into a mass of mercurial spears. All creatures within 15 ft. must make a Dexterity saving throw (DC 16). On a failure, they suffer 10d6 piercing damage and are blinded until the end of their next turn. 
2-20: The item takes on a different form, determined by the DM. All attacks are made with a disadvantage.
21-40: The item does not receive any additional effects.
41-50: The item becomes imbued with the strength of flames. The weapon now deals an additional 2d4 fire damage on top of the original damage.
51-60: The item becomes imbued with the vigor of the mountains. You and all creatures of your choice within a 10 ft. radius centered on you gains a +1 bonus to their AC.
61-70: The item becomes imbued with the darkness of shadows. Stealth checks are now made with advantage. As a bonus action on subsequent turns, you can teleport to any shadow within 60 ft. of you.
71-80: The item becomes imbued with the sharpness of steel. You now have a +2 bonus to attack and damage rolls made with this weapon.
81-90: The item becomes imbued with the haste of lightning. Your walking speed doubles and you gain the benefits of having Extra Attack (stacks with other Extra Attacks).
91-97: The item transforms into a bayonet rifle. The rifle can make a melee attack that deals 2d6 piercing damage (Vex). The rifle can be fired in bursts (150 ft./300 ft.) that deal 10d4 piercing damage. The rifle can be fired as a silenced sniper (300 ft./500 ft.) that deal 5d10 piercing + 2d8 force damage. On a range attack roll of 1-3, the rifle jams and will be rendered useless for the rest of the duration unless you use an action to make a DC 15 Tinkering (Intelligence) check.
98-99: The item begins to completely synergize with the user. You can choose whichever effect you desire from the table (except 100).
100: The item violently releases a huge amount of arcane energy as it merges with your Trusty Mount and begin to transform into a Huge Mech. The Mech has an Armor Class of 18, Hit Points equal to 100, Walk Speed of 40 ft. and the following abilities:

Has access to the 71-80 effect
Flamethrower (BA). Dexterity Saving Throw (DC 16) 3d8 fire damage in a 15 ft. cone whenever a creature enters the area or starts its turn inside it. On a success, the creature only suffers half the damage. The cone's direction can be changed as a Bonus Action.
Shield (A). Immediately gain 3d10 temporary hit points.
Chainsaw (A). 4d10 slashing damage. Strength Saving Throw (DC 16) or the target is knocked prone.
Rockets (A). Designate a 5 ft. wide, 20 ft. long line. Creatures in this area must make a Dexterity Saving Throw (DC 16) or suffer 8d6 fire + 2d8 force damage.

Additionally, at the end of every turn the Mech is active, roll a d6. On a 5-6, the Mech suffers 2d6 fire damage. This damage cannot be reduced in any way for the mech and half of which will be dealt to any creature currently in contact or inside the mech.

Once this feature is used, you cannot use it again until you complete a long rest.

Notes: Highway Rider Rogue