Since the sinking of Arenel, developments in making the underwater world safer to traverse are more rapid than ever, and a particular government-funded endeavor has led to the invention of Diving Bells. These hulking mechs are built to last and withstand the dangerous conditions of the deep. While diving bells weren't initially built for combat, their hulking power can be a valuable ally to a party and can be upgraded with special attachments and weapons. An Aquatic Mechanicus pilot is responsible for the management and upkeep of such mechs, even becoming attached to them after a while, giving them names and custom paint jobs to match their pilot. Aquatic Mechanicus can be relied on to do the heavy lifting in underwater exploration, and have a variety of additional skills to help defend their allies and make quick repairs. 

Tool Proficiency

3rd-level Aqua Mechanicus feature

You gain proficiency with smith’s tools and water vehicles. If you already have either proficiency, you gain proficiency with one other type of artisan's tools of your choice.

Aqua Mechanicus Spells

3rd-level Aqua Mechanicus feature

You always have certain spells prepared after you reach particular levels in this class, as shown in the Battle Smith Spells table. These spells count as artificer spells for you, but they don’t count against the number of artificers spells you prepare.

Aqua Mechanicus Spells

Artificer Level	Spell
3rd	heroism, shield
5th	spider climb, warding bond
9th	water walk, clairvoyance
13th	resilient sphere, fire shield
17th	arcane hand, wall of force

Diving Bell

3rd-level Aqua Mechanicus feature

Your tinkering has constructed a Diving Bell, a hulking mechanical suit ready for deep-sea exploration. It has no will of its own, and it requires a pilot to function. See this construct’s game statistics in the Diving Bell stat block, which uses your proficiency bonus (PB) and spellcasting modifier in several places. The Diving Bell's stats reflect your stats and do not change if there's a different pilot. You determine the construct's appearance and whether it has two, three, or four legs; your choice has no effect on its game statistics.

In combat, the Diving Bell shares your initiative count, but it takes its turn immediately after yours. It can use reactions and move on its own, but it requires a pilot to use actions/reactions. A pilot can move the mech as a mount, and it can use an action from its stat block or some other action. If the pilot is incapacitated or otherwise unconscious, it will take the dodge to protect the pilot. While not in combat, the Diving Bell will automatically follow you as long as it can find an appropriate path to you.

If the mending spell is cast on it, it regains 3d6 hit points. If it has been destroyed within the last hour, you can use your smith’s tools as an action to revive it, provided you are within 5 feet of it and you expend a spell slot of 1st level or higher. The Diving Bell returns to life after 1 minute with 1d10 hitpoints.

You can begin to create a new Diving Bell at the end of a long rest, assuming you are in a dedicated workshop and have smith's tools. Constructing a Diving Bell takes 2d6 days and requires at least 500gp. You can reduce this time by 1d6 days and 250gp if you are using a decommissioned Diving Bell for parts. If you already have a Diving Bell from this feature, the first one immediately perishes. The Diving Bell also deactivates if you die, requiring a new pilot to reactivate it.

Arcane Attatchment

 

3rd-level Aqua Mechanicus feature

Your experience maintaining your Diving Bell has led you to build improvements for it, granting it additional abilities and actions. At the end of a short or long rest, you may use your smith's tools to create an arcane attachment. Your arcane attachments can be mounted on your Diving Bell's arm or shoulder; although this doesn't affect its in-game statistics.

You may choose from the following options:

Arcane Shield. Created to protect Diving Bells from falling rubble, a projected magical shield can be the difference between life and death.

Harpoon. Since Diving Bells have trouble swimming, harpoons were designed to help grapple and climb vertical surfaces. Still, the harpoon is an effective ranged weapon.

Mining Drill. Many of the new materials beneath the seabed are difficult to harvest, so drills became a necessity. Even then, a creature shouldn't want to be on the other end of it.

Once you create an attachment, you can’t do so again until you finish a long rest or until you expend a spell slot to create one. You can have only one attachment at a time and can’t create one while your attachment is present.

While piloting your mech, you can use an action to activate your arcane attachment a number of times equal to your proficiency bonus for each long rest. 

Attachment	Activation
Mining Drill	Upon activation, you may make a melee spell against a creature within 5 feet of you. On a hit, deal 4d6 slashing damage. If the target is medium or smaller, they must succeed in a DEX save equal to your spell save DC or be incapacitated until the end of their next turn.
Harpoon	Upon activation, you may make a ranged spell attack at a creature within 60 feet of you. On a hit, deal 2d8 piercing damage, and if the creature is medium or smaller you may pull it 5 feet towards you. The harpoon can extend to 100 feet and can hook onto objects similar to a grappling hook.
Arcane Shield	Upon activation, the Diving Bell grants a +2 AC to itself and up to two allies within 5 feet of you.

 

You may build one additional arcane attachment at level 15.

Explorer's Conduit

5th-level  Aqua Mechanicus feature

Your Diving Bell has become a conduit for your spellcasting. When you cast a spell and are within 30 feet of your Diving Bell, you may add a 1d4 to one healing or damage roll associated with the spell. 

Big Daddy

9th-level Aqua Mechanicus feature

Your Diving Bell has become stronger over time and now is both stronger with an added last resort. 

The Diving Bell's attacks deal an extra 1d8 force damage.

You may command your Diving Bell to self-destruct. As an action, you may cause it to drop to 0 hit points and force all creatures within a 30-foot radius to make a DEX save (against your spell save DC) or take 8d6 force damage on a failed save or half as much on a successful one. All ground in the radius becomes difficult terrain, and nearby objects are destroyed.

The extra damage your Diving Bell deals increases to 2d8 at level 15.

Reinforced Hull

15th-level Aqua Mechanicus feature

Your Diving Bell becomes more powerful:

• The extra damage from Big Daddy increases to 2d8
• Your Diving Bell gains a +2 bonus to Armor Class.
• You may build one additional Arcane Attachment for your Diving Bell.