This idea came up in discord where I was complaining that my 5e familiar isn’t ever going to be as cool as my 3e one. Looking into it, I realized 5e doesn’t do much at all with them, except have them be cool little guys who hang around. This subclass is designed to fix that. It won’t let you have a sentient creature who marches around next to you with full plate, a reach weapon, and be better at fighting than your fighter friend, but it will let you play something fun. And that’s what we are all about here.

Familiar Trainer
The path of the familiar trainer is one that emphasizes the special bond of an arcane caster, and their magical familiar. While all wizards can form a bond with a familiar, the Trainer takes it a step further, allowing the familiar unparalleled freedom in exchange for enhanced power.
Obtain Familiar: At second level, you automatically add the spell Find Familiar to your spellbook, if it is not already. Additionally, you have direct permission to dumpster dive the various monster books for cool familiars like Imps that say it’s allowed in the variant sidebars but not in the Find Familiar spell.
Combat Familiar: At second level, if your familiar is in the same space as you, you can use your reaction to have your familiar take an attack of opportunity whenever you would normally be entitled to one. Additionally, you can always occupy the same space as your familiar, regardless of both of your sizes. One of you can ride the others shoulders, or its a 5ft square, there is plenty of space
Familiar Ward: You like your little guy and don’t let bad stuff happen to him. At second level, once per point of proficiency modifier each long rest, whenever your familiar would take damage, you can choose to take half that damage for them, provided you have line of sight.
Improved Familiar: At 6th level, when casting the find familiar spell, you can select from an improved list. You can summon any of the following creatures to act as your familiar. A giant eagle, scarecrow, fire snake, hippogriff, or spectre. Note, this does not apply to the Flock of Familiar spell, or similar spells or abilities that reference the find familiar spell.
Greater Familiar: At 10th level, you gain the ability to select a familiar from a greater list. A mimic, faerie dragon (choice of color), pentadrone, ocre jelly, Pegasus, will-o’-wisp, spined devil, or awakened tree.
Master Familiar: Starting at 14th level, you gain the ability to select a familiar from a master’s list. A spectator, giant scorpion, wyrmling dragon (without spells), hellhound, bearded devil, owlbear, or wight.