Clyde the Giant Crab

Amphibious. The crab can breathe air and water.

Battle Readiness. The sidekick has advantage on initiative rolls.

Indomitable. The sidekick can reroll a saving throw that it fails, but it must use the new roll. When it uses this feature, it can’t use the feature again until it finishes a long rest.

Improved Critical. The warrior’s attack rolls now score a critical hit on a roll of 19 or 20 on the d20.

Draconic Senses. You gain keen senses like a dragon’s. Blindsight. Your blindsight increases by a range of 10 feet. Keen Senses. You have advantage on Wisdom (Perception) checks.

Special Equipment. Clyde wears hat of wizardry and carries a staff of striking with 10 charges. The staff regains 1d6 + 4 expended charges daily at dawn. If its last charge is expended, roll a d20; on a 1, the staff becomes a nonmagical quarterstaff.

Firebolt. You hurl a mote of fire at a creature or object within range. Make a ranged spell attack against the target. d20+4. On a hit, the target takes 3d10 fire damage. A flammable object hit by this spell ignites if it isn't being worn or carried.

Booming Blade. You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects plus 2d8 thunder damage and then becomes sheathed in booming energy until the start of your next turn. If the target willingly moves 5 feet or more before then, the target takes 3d8 thunder damage, and the spell ends.

Extra Attack. The sidekick can attack twice, instead of once, whenever it takes the Attack action on its turn.

Claw. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 2) bludgeoning damage, and the target is grappled (escape DC 11). The crab has two claws, each of which can grapple only one target.

Shortsword. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 4) piercing damage.

Staff of Striking. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 8 (1d6 + 5) bludgeoning damage, or 9 (1d8 + 5) bludgeoning damage when used with two hands, and Clyde can expend up to 3 of the staff's charges, dealing an extra 3 (1d6) force damage for each expended charge.

Second Wind. The warrior can use a bonus action on its turn to regain hit points equal to 1d10 + its level. If it does so, it can’t use this feature again until it finishes a short or long rest.

Shield. An invisible barrier of magical force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from Magic Missile.