Magical construct

An ancient artifact designed to protect certain locations. It consists of large rocks covered in metal plates, held together by strands of blue light in a humanoid form.     Stats:   Armor Class 16 (natural armor) Hit Points 120 (20d10 + 10) Speed 30 ft.   Str: 20 (+5) Dex: 13 (+1) Con: 16 (+3) Int: 1 (-5) Wis: 12 (+1) Cha: 1 (-5)     Skills:   Perception +5 Damage Resistances Lightning, Cold, Fire, Piercing, Acid, Radiant, Necrotic, Thunder. Damage Immunities Poison Condition Immunities Poisoned Senses Darkvision 120 ft. Languages None Challenge 5 (1800 XP)     Traits   Punch: Range: 5 ft. Melee attack. +5 to hit. Deals 2d6 bludgeoning damage.   Form shift: The magical construct can switch between offense and defence mode as an action, costs 3 charges.  

• In offense mode the construct drops their AC to 14. When hit by a non-magic attack the construct gains charges equal to 1 + (damage taken / 3) (rounded down).
• In defence mode the construct increases their AC to 16 but decreases their movement speed to 20 ft. When hit by a magic attack the construct gains charges equal to 1 + (damage taken / 3) (rounded down).

  Offensive mode traits:   Magic blast: Costs 4 charges. Range: 10 ft. Deals 2d8 force damage. A magic blast covering a cone in front of the magical construct. Any creature in range must make a DC 14 Dexterity saving throw. If the target succeeds the save they only take half damage. If they fail the save they take full damage and are knocked back 5 ft. Cannot be used two turns in a row.   Reverb: Costs 8 charges. Range: 10 ft. Deals 25% max health force damage. The pent up magical force in the construct explodes violently all around, affecting everyone in range. Any creature in range must make a DC 15 Dexterity saving throw. If the target succeeds the save they don't take any damage but are pushed back to a maximum of 10 ft. from the construct.     Defensive mode traits:   Magic reinforcement: Costs 4 charges. Range: 5 ft. Deals 1d6 bludgeoning damage. +5 to attack. On a hit raises the AC of the construct by 1 until their next turn. The construct siphons the life energy of a nearby creature to amplify its defence. Cannot be used for two turns afterwards.   Magic mend: Costs 10 charges. The construct regains 20 hp but cannot gain charges until they are back down to the health they were before activating Magic mend. Cannot be used again until the construct has entered offensive mode.   Malliable: Costs 5 charges. The construct becomes resistant to the last damage type dealt to it for 3 turns. Cannot be used for 5 turns after use.