Elemental, I choose you!

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I think it'd be pretty cool if you're fighting an elemental, and, instead of killing it, you throw a pokéball at it and capture it. Then you treat it like a pet and toss it out to fight for you. 

(I've been thinking about elementals a lot because I'm running Princes of the Apocalypse; listen to our campaign over at gg no re: http://ggnorecast.blogspot.com.) I'm thinking of putting these in our game. If you use them, let me know. 

Table of contents:

1. Using them
2. Creating them
3. Generalizing the concept, for full on pokemans: TERATOSPHERES
4. A class: the KETCHUM

CATCHING THEM ALL

You must attune to the ball in order to use it. if you're not using D&D 5e, you can't use more than 2 other serious magic items while you're using a stoichesphere. Magical interference or something. 

While you hold it against your skin and consider an elemental creature, the stoichesphere haptically alerts you to the current strength of the elemental's coherence. This means that, If it's below half hp, the GM will tell you exactly how much hp the creature has left. 

Toss it at an elemental creature within 30'.  

The elemental makes an hp save vs the sphere's DC. Making an hp save means rolling a d20 and adding the creature's current hp to the roll.  

If the creature makes its save, the spell flares out of the sphere, but the creature is yet too coherent to be contained. The spell fails, and the ball is now inert until dawn.  

If the creatures fails its save, you caught it. 

If the creature hits 0 hp before you catch it, sorry! OR: you get one shot this round or the next to catch it before it fully dissipates.

IGNIS, I CHOOSE YOU!

You must be attuned to the ball in order to use its creature in combat. 

Name the captured creature in order to use it in battle. 

To make it fight for you, toss the ball within 30' of you and say earnestly, "[creature name], I choose you!" It fights as a normal creature and recovers hp in exactly the same way PCs do in your campaign. 

The ball flies back to the caster's hand. The caster now controls the creature.  

It shares your turn and will do whatever you say, but it will do nothing unless you issue a command properly: "[creature name], [command]!" Don't forget the exclamation mark when you say it. It doesn't really have an action economy, per se. You get one command per turn (just based on the six second round, and how much time you have to talk), and it does whatever is necessary and possible to complete it. So you don't have to command it separately to move and attack. Just tell it to attack or come back to you or whatever, and it'll do its best.

If the creature goes to 0 hp, it dies, and its ball shatters. Perhaps it looks at you with big sad eyes. 

You can recall the creature by command. 

CREATING THEM

When an elemental creature dies, it leaves behind an elemental mote that remains for an hour unless stored properly, e.g., in a stoppered glass vial. They are subtle and easy to miss unless you're looking for them. These are the components of the ritual to create a sphere. Note the HD of the creature that left the mote behind. This is the potency of the mote.

In order to be able to create stoichespheres at all, you must know the ritual. These are contained in schemata that the GM will place as treasure (or in shops possibly; see below). The schemata detail how to make the sphere and the spell required to imbue it with the relevant magic. 

Any blacksmith can look at the schema and can create the object with a gold and a day, and any arcane caster can learn the ritual. 

You need a suitable lab or arcane study. Surround / immerse it with the proper elements (burning fires, troughs of water, a dozen servants waving fans—the DM will tell you what). 

Then decide which of your motes you will use as components. This determines the save DC of the sphere. 

You must also expend a number of spell slot levels equal to the potency of the strongest mote used. Multiple casters can help to share the spell slot expense load. 

The base DC is equal to:

caster's proficiency bonus* (x2 if all motes used are of the same element)

+ 

potency of strongest mote used

Thus a level 1 caster (prof bonus +2) who is performing the ritual with only an HD 5 elemental creature's mote will create a sphere with a save DC of 4 (prof bonus of 2, x2 since all motes are of the same element) + 5 = 9. The caster would need to expend 5 levels of spell slots, split up however: 2 level 2s and a level 1, for instance. 

To increase the save DC beyond the base, you can add additional motes. Total the potencies of the lesser motes you are combining and divide by the potency of the greatest mote, rounding down. Add the result to the DC. You can't add more than 5 to the DC this way. 

Example 1: You have 4 motes, each of potency 5 (these were 5 HD fire elementals). The greatest mote is set aside (since they're all the same, it doesn't matter which one we choose). This means, with our example above, we have a base DC of 9. But now we have 3 "lesser" motes to add into the mix. We sum their potencies and get 15 (5 + 5 + 5). We divide 15 by the potency of our "greatest" mote (5) and get 3. That's what's added to the DC for a total DC of 12. 

Example 2: a level 1 caster (prof bonus 2) is going to create a stoichesphere using a greatest mote of potency 6. Base DC = 6 + 2 = 8. Caster has 5 other motes, of potencies 2, 3, 3, 4, and 5. These motes are a mix of fire, water, air, and earth. Summing those together we get 17. 17 divided by 6 (the potency of our greatest mote) gets us 2, rounded down. So probably the caster will want to reserve her potency-5 mote for later so as not to lose it to rounding. Removing that, we have a lesser total of 12, divided by 6, equaling 2 on the dot. We add that to the base DC of 8 for 10, again. Note that, because we used motes of different elements, we don't double the proficiency bonus when calculating DC.

BUYING THEM

If you can buy magic items in your game, these would be considered common to rare, depending on how plentiful and strong elementals are in your setting. Maybe 50g per point of DC. Schematics cost a flat 1000g.

You might also find elemental motes for sale. I'd say maybe 50s per HD, times the proficiency bonus* of the creature. I don't know. That number is mostly made up off the top of my head.

PLACING THEM AS TREASURE

Elemental cults will have them, as will wizards and magic merchants. Ruins of old cities, especially underdark cities would have them, as well, more rarely, schematics for them.

GENERALIZING THE CONCEPT

It should be reasonably clear how to turn this into all the way pokemans:

• elemental mote > most iconic piece of carcass
• "elemental" > creature type 

For instance, say you find the schema for creating a goblin-ball. This will capture goblinoids (goblins, hobgoblins, orcs, bugbears, orogs, ogres maybe). Their "mote" is the liver, maybe, or the stomach, or the eyes. Try to find something evocative. Maybe goblins are iconic for their greed in your campaign. Then choose the part that most represents that: the eyes maybe, or the stomach. Then that's what the schema tells you that you need to grab. If you use all goblin eyes, then double your prof bonus, and the ball works only on goblins (or, don't double your bonus and have it usable against orcs too). 

If you're using generalized balls, maybe call them TERATOSPHERES.

A CLASS: THE KETCHUM
This is just the skeleton of the class; I don't really care to go into the fine details now.

• HD as wizard
• no armor
• +1/12 of XP needed for next level when you catch a new monster and add it to your teratotome (see below); this is the small quest XP award in the 5e DMG if you just want to use the chart
• simple weapons like slingshots and sticks and stuff you might find at a disused park or an old shack
• when you do damage, your dice is of the same size as your HD
• no multiclassing
• primary stat: charisma
• good saves: charisma, wisdom
• survival, nature, perception
• goal: wants to catch them all and be recognized as the best
• flaw: gotta catch em all
• flaw: attracts rivals who try to foil plans, steal teratospheres, and show the ketchum up; the ketchum must save or try to do the same
• bond: Magister X, who gave you your first teratosphere, containing your first monster
• bond: your first monster
• bond: your rival
• bond: your first teammate
• item: your teratotome, which has the notes from all the monsters you've caught; if you actually keep a physical teratotome with you and updated, gain +1 HP / level. 
• teratospheres don't count against attunement limit
• can be attuned to a maximum of [proficiency bonus] spheres at once
• your sphere DC is 8 + Charisma mod plus proficiency bonus; this puts a floor on the sphere DC of spheres you use; the save DC can never be lower than your personal DC
• starts with 1 sphere and 1 creature, HD 1 probably, name it
• your creatures don't die when reduced to 0 hp, and your spheres don't shatter; instead, the creature returns to the sphere and is exhausted and can't be roused until dawn
• however, if the teratosphere is destroyed, your creature is too; the sphere is just as strong as the material it's made out of; give it an appropriate AC value + 5.
• you don't need schemata; you got this naturally
• you don't need to spend spell slots (you don't have them and can't gain them) to enchant pokeballs; you are born with THE TOUCH and simply hold the ball in one hand and the motes you wish to use in the other, and wham, there's your teratosphere
• EVOLVE: your monsters level with you. 
• They get the same XP you do as long as they participated 
• They level by the same scheme as you, where HD = level
• When they level, they get another HD (and thus more hp)
• When they level, you learn something about them that you write in your teratotome
• this is an opportunity to come up with something smaller that's still fun: 
• it's tougher than it appears because X: +1 AC
• it's stronger than you'd think: +size to damage die
• you can only make such a discovery once about a creature
• When its proficiency bonus increases, the creature evolves
• you learn a big feature about it: multiattack, elemental damage, etc. 
• you give this evolution of it a particular name

* 1 + # of caster's HD / 4, rounded up