Wicked Obsideon (5e Creature)
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Tough As Rocks. The Obsideon takes no bludgeoning damage as a result of falling if it is not incapacitated. Additionally, when it is unarmored, the Obsideon's AC is 13 + its Dexterity modifier, included in its above AC.
Flesh Crafting. The Obsideon is indistinguishable from a normal humanoid with an appearance of its choice while it has more than half of its hit points. As an action, it can change its appearance or reveal its true form. When it changes its appearance this way, the Obsideon can't change any of its physical traits, such as its height, weight, amount of limbs, etc.
Construct Nature. The Obsideon doesn't require food or water, doesn't age, and can't be aged by magical means.
Fool's Gems. When the Obsideon dies the bones in its body disintegrate into worthless gem dust which cannot be used for spells.
Calculated. The Obsideon can choose to reroll a failed attack roll, ability check, or saving throw. Once it has done so once, it cannot do so again until it finishes a long rest.
Summon The Blade. The Obsideon can use its bonus action to turn one or both of its arms into living obsidian blades, or to return them to normal. These blades are considered to be longswords and the Obsideon is proficient with using them. While its arms are transformed this way, the Obsideon cannot use them for anything else other than as blades. The Obsideon can perform the Somatic components of spellcasting with its arm blades.
School of Abjuration. The Obsideon can use all of the features of the School of Abjuration subclass for the Wizard class, detailed in the 5e PHB.
Linguist. The Obsideon can create written ciphers. Others can't decipher a code it creates unless it teaches them, they succeed on a DC 26 Intelligence check, or they use magic to decipher it.
Tough. The Obsideon has an additional 40 hit points, regardless of using the average hit points (Included in the above hit point total) or rolling hit points.
Spellcasting. The Obsideon is a 20th-level spellcaster. He has 20 levels in School of Abjuration Wizard. The Obsideon can prepare the following Wizard spells:
Cantrips (at will): fire bolt, mold earth, prestidigitation
Arm Blades. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 10 (1d8 + 5) slashing damage.
Poise. The Obsideon uses its reaction to avoid damage from a melee or ranged weapon attack.
The Obsideon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Obsideon regains spent legendary actions at the start of its turn.
Spellcast. The Obsideon casts a spell.
Legendary Initiative (Costs 3 Actions). The Obsideon takes an extra turn. It does not regain legendary actions on this turn, and does not change its initiative for its normal turn. During this turn, the Obsideon does not provoke opportunity attacks. Once this Legendary Action has been used 3 times, it cannot use this Legendary Action again until the Obsideon finishes a Long Rest.