Artificer's Rogue Training Dummy

Desperation. While not designed to output a lot of damage, the Training Dummy's sole purpose is to win combat encounters. When below 10HP, it is able to use two actions in one round of combat, and it gains +2 to its AC. 

Quick Learner. This opponent learns to deal with predictable attacks. If a player uses the same weapon or spell numerous times, they become less effective in accordance with the below (note, weapons with multiple uses like daggers (which can be melee or ranged) have distinct "uses" for each type; the same is true for weapons that can be wielded with one or two hands):

Weapons:

• 1st use - Works as intended
• 2nd use - Disadvantage on attack rolls
• 3rd use - Attack modifiers are removed
• 4th use - Attack modifiers are removed and disadvantage
• 5th use and beyond - Can only be hit on a Nat20

Spells:

• 1st use - Works as intended
• 2nd use - Disadvantage on attack rolls; Training Dummy has advantage on spell saves
• 3rd use - Attack modifiers are removed; Spell save DC now capped at 11
• 4th use - Attack modifiers are removed and disadvantage; Spell save DC now capped at 11, and Training Dummy has advantage on spell saves
• 5th use and beyond - Can only be hit on a Nat20, Cantrips cannot hit; Automatically succeeds any spell save for Cantrips & Level 1 Spells; Spell save DC now capped at 6. 

Spellcasting. The Training Dummy has following spells prepared:
Cantrips (at will): Fire Bolt (You hurl a mote of fire at a creature or object within range (120ft). Make a ranged spell attack against the target (+2). On a hit, the target takes 1d10 fire damage. A flammable object hit by this spell ignites if it isn't being worn or carried.)

Vulnerable to Novelty. If an player chooses an avenue of attack that the DM considers absurd but plausible, the DM can grant the player advantage or a similar boost, and can temporarily deactivate relevant Reactions that the Training Dummy could otherwise employ. 

Creation. The Training Dummy has a creator. Upon its defeat, a magical rune appears on its forehead, along with a magical broadcast ** Repairs needed - please press rune to return device to the workshop ** If pressed, the Training Dummy will levitate, and move towards the workshop. 

Action Melee Attack. Training Sword: +4 to hit, reach 5 ft., 1 target. Hit: 1d6 + 2 slashing damage.

Action Ranged Attack. Dexterity Training Darts: Automatically hits against opponents with a Dexterity stat of 13 or below, or prone opponents. Otherwise, +2 to hit, range 60 ft., 1d4 target(s). Hit: 1d4 + 1 piercing damage.

Action: Analyze & De-Escalate. ** Primarily for use early in the encounter, when the Training Dummy is not yet sure of the prowess of its opponent. ** Instead of attacking with the intent to seriously harm, it instead uses the flat side of its sword to powerfully launch its target 15ft away. The target must succeed a Strength Saving Throw of DC 13 to resist. On a fail, they move the full 15ft and take 1d4 damage. On a success, the move is less effective, pushing them only 5ft and out of combat. However, the Training Dummy is now aware that a success means an opponent is strong, and will be more likely to target this opponent (and less likely to hold back its attacks).

Adapt & Recover. If the Training Dummy has taken damage from one of the following since its last turn in combat, it can choose a corresponding bonus action:

• Spear; Dagger; Handaxe - Recover 1d4 HP
• Crossbow (Light or Heavy) - Gain +1 AC against ranged attacks until its next turn
• Shortsword, Rapier, Scimitar, Longsword - Gain +1 to any melee attack rolls this turn

Mimic Fighting Style. The Training Dummy chooses one target within range to emulate. It can choose one of that target's actions to learn (melee attack or ranged attack) for the duration of its turn. Its "training sword" shimmers with magical light and transforms into the weapon associated with its target's action, and it gains all associated stats for the duration. 

Counter Strike. When hit with a melee attack from a specific weapon it has encountered before (i.e. a player's scimitar, not all scimitars), it will imitate the strike exactly: with the same dice roll to hit. 

Patient Block. The Training Dummy covers up with a patient guarding stance. It takes half damage until its next turn, however it loses the ability to use any bonus actions on its next turn