So What Are Familiars?
Familiars are summonable monsters that can be ordered to prioritize certain actions, such as defending, attacking, applying group buffs (if able to), or either one of the three options automatically. Below is a rough sketch of what the options would look like in game.
How Are Familiars Obtained?
Familiars are obtained via killing normal, dungeon, and event enemies, with exceptions to certain bosses and enemies. Droprates would vary, but it would be around a 5-7%drop chance for most enemies, Usually dropping in a yellow bag. As for eligible bosses, they would be more akin to a 1-2% drop chance, dropping in white bags. In these bags, however, will not be the familiar itself, but its summoning stone used to unlock it. These summoning stones WILL NOT be tradeable for obvious reasons.
After Finding A Summoning Stone
Once you’ve obtained a summon stone from say a Sea Horse: 
The summoning stone would look something like this (depending on the monster)
All you would have to do is use it like a regular consumable, and voila, you have added the familiar to your familiars library. Stones of an already obtained monster can be used later for upgrading your familiar.
The Familiar Library
This “Library” can be accessed through the vault from this pocket portal next to the wardrobe
as seen here:
From here you can click the “Choose” button when you stand next to the familiar library to be shown the familiars page. from here you can see, enhance, check your familiar roster’s stats, and pick all of the familiars you unlocked and take with you as seen here in this example:
(Quick note: You can’t get more than one of the same monster, sorry urgle lovers.)
Picking Familiars
When you’ve reached the screen above you simply have to double click on the desired familiar, wait a bit and you will get a notification confirming you have successfully added the familiar to your familiar roster.
The familiar roster
The familiar roster can be accessed either at the familiar library or to the right of the pet icon, from here you can see your chosen familiars, check their stats/levels, and of course summon them by double clicking on your desired familiar.
Familiar Abilities
Now we get down to the fun part, this sets familiars apart from pets because of three very important aspects.
Familiars grow with you! (Stat wise)
Familiars will gain a %1.5 percent bonus to their specialized abilities for every 1 maxed stat of your character. This leads to a maximum of 12% effectiveness in your familiar’s abilities. There’s also the idea of a 0.25% increase for every 200 base fame gained on your alive character, maxing out after 2000 base fame.
Familiars have unique abilities based on their monster.
most familiars will have preset abilities that will be the same for all players who first unlock them, eliminating the randomness of pet hatching. second of all, almost all familiars would have abilities based around their monster. Monsters such as the Deadwater Docks Commander will have attacks similar to their normal versions, but will be spiced up in order to aid the player. In the case of the DDocks Commander, his throwing bottle attack would be changed to do AoE (area of effect) damage to enemies who step its contents, or a buff from the rum that increases attack but adds drunk.
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More interesting monsters like Champions of Oryx can provide group buffs to aid players (buffs don’t stack btw). Boring cannon fodder get defensive abilities such as minor life steal and offensive abilities to boost overall usefulness in battle. Tanky monsters will be able to deflect damage the player takes to itself, damaging it, but also leaving the player unscathed, that is until the familiar eventually dies from taking too much damage. As for how familiars use their abilities would be based on what priority you set them to and if they have the abilities to do that action.
Familiar enhancement
To the left of the Exit option in the Familiar Library is the Familiar Enhancement page. This page allows you to select the familiar you want to enhance from the library and either upgrade the familiar’s abilities, upgrade the familiar directly, and add or remove abilities from the familiar with familiar essence as shown here.
What the hell is familiar essence and ascension??1?
Familiar essence is a separate “currency” from fame and is gained from consuming summoning stones (the amount of essence increases if the stone is rare), getting consumable that give familiar essence, or by feeding familiars items, unlike feeding pets, this will not cost any fame or gold. Instead, fame can be used to increase the amount of essence given from items, up to +1/2 the amount of familiar essence of the item on top of the original amount (ie 150 fame for 1/10 ), gold does the same except its twice as much at a discounted price, up to original the amount familiar essence on top of the original amount (ie 50 gold for 2/10) (Cuz this has to be monetized somehow). As for familiar ascension, this is only available once your familiar has reached level 50 and you have 65000 familiar essence to spend. from there, you unlock 1 free special ability from 3 of your choosing, 25 extra levels, and an increase to familiar stats by 5%.
Upgrading Your Familiar
After clicking the “Upgrade Familiar” button, you will be taken to a page that shows the overall stats of your familiar and the upgrade button with the required amount. The amount of essence required to enhance is increased by a fixed amount on a fixed starting amount every level. starting amount depends on familiar, lesser familiars require less essence and vice versa, fixed amount also varies from familiar.
Edit 3/9/19:
regarding familiars’ max stats, this varies, but familiars will always gain 1 point in each stat per level. Once a stat has been maxed (for Stheno’s Pet, probably 24 ATT, 37SPD, 32 DEX, and 15 absorption) they will increase by 1 every 5 levels (special stats would not increase after maxing). A familiar’s overall stats would increase by +9 after reaching max level.
Upgrading Your Familiar’s Abilities!
After clicking the “Upgrade Ability” button, you will be taken to the abilities page, here you can select and enhance effectiveness, duration, damage, AoE, spread, etc by a fixed percentage (around +1/8 of its starting stats). The cost amount for abilities is determined by what level they are and how far down they are in the tree (they’ll usually be around 2000-5000 to purchase and upgrade them). You can do this up to a maximum of 5 levels for a ability, after which it will not be upgradeable. This is also where you can unlock new abilities for your familiar to use. The abilities will also display a short description of what they do and what stats they affect. Lastly, pressing enhance under the description will show you how much it will increase by, cooldowns, overall stats and a confirmation to do that action. (Note: as the level of the ability increases, so does the cooldown, so it’s wise to not level abilities up if the familiar isn’t up to a sufficient level).
Adding And Removing Abilities
Last but not least, is the ability to actually use and remove your abilities. Simply choose whether or not you want to remove an existing ability from your familiar’s ability list, and select your ability of choice, it’s self explanatory really.
Familiar Restrictions
Overcrowding
Because of how overcrowded the game already is, Familiars can only be summoned for about 3-4 minutes, and have a cooldown of 3-5 minutes after the familiar has expired, mostly to prevent players’ frames from dropping to -0. And on top of that, if you want, you can completely hide all familiars except your own if it gets too laggy 
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Summoning
To prevent lag and keep overall balance in game, only 1 familiar can be summoned at a time, and once you have summoned a familiar you cannot change it until the cooldown is over.
Number of familiars
you may have 3 normal familiars, but only one boss familiar is allowed in the roster. You obviously cannot have more than 3 familiars in your roster ever.
Familiar library
As I’ve mentioned before, only most of the monsters in game will be able to be gained as familiars, mostly due to balancing reasons. Examples of unobtainable monsters are:
- Almost all endgame bosses (with the exception of the Stone Guardians)
- A few of the early-midgame bosses (probably around 3 for early and 4ish for midgame)
- Some lower tier endgame monsters such as ice mage.
- Spooky Boi (MAYBE)
- Most event gods (except some of their adds)
- Certain adds from monsters such as paper golem, sprite children, etc
- Monsters that spawn adds when killed (Depths eggs for example)
- All misc monsters (except piñata maybe)
I’ll add more to the list if the need arises
Conclusion
The whole inspiration of my magnum opus was from a combination of other MMO RPGS, Crafting/Enhancement systems from games like Destiny, The drake eggs in Rotmg, and from some of the amazing ideas this community has made so far. As of writing this conclusion, I worked on this for 8 hours straight and I regret it, but in a good way. If you made it all the way down here, then I congratulate you, because this is some long hit. Anyway, all feedback is welcome and appreciated, and thank you for reading 
Edit 3/9/19: added clarification for maxing familiar stats