The Aviator archetype takes the standard mount and rider relationship to a new level - literally.  You and your chosen mount make for an incredible combat team. Your flying mount is incredible in the open air and as you gain levels you learn how to use it inside buildings.  As you grow in power, you can upgrade your mount to a larger more powerful version.

While lances are traditional, Aviators are famous for liking ranged weapons.    They are quite capable of using both hands to attack while using their legs to direct the mount to move.  

 

Mount

At 3rd level you gain a flying mount that can take you anywhere.  Choose a beast from the chart below.  Add your proficiency bonus to the Beasts' AC, attack and damage rolls as well as any saving throws and skills it is proficient with.  It 's max hitpoints equal the stat block or 4x ranger level, whichever is higher.   It can spend HD during a short rest. 

Also, the spell "Feather fall"  is automatically added to your ranger list,  learned by you and does not count against the spells known.

Your mount obeys your commands as best it can, moving on your initiative, effectively granting you it's speeds.  You can use an action to command it to make one attack, dash, disengage, dodge or help.  Otherwise it only attacks creatures that try to hit it.

If you are incapacitated or absent, the beast acts on it's own, focusing on protecting you and itself.  It never requires your command to use it's reaction.   When traveling through your favored terrain with only your mount, you can move stealthily at a normal pace (i.e. attacking from above(

 If the beast dies you can obtain a new companion after a long rest, if you start the rest magically bonding with a creature that is not hostile to you and qualifies.

Your mount must be one size larger than you.  A Medium Mount can carry you and 60 lbs of weight.  A Large Mount can carry you and 90 lbs, a Huge Mount can carry you and 120 lbs, without lowering it's fly speed.  Half speed Movement is possible when carrying up to twice that amount (so you and one other person and 180 lbs for Large), but anymore and you are not flying.

Mount fly speeds are for open areas.  If you take a Medium sized beast into a building designed for Large  sized walking creatures (20 ft hallways, 20ft ceiling) , it has full flight speed.  If you take it into a building designed for medium sized walking creatures (10 ft hallways, 10 ft ceiling)  it can fly, but it  has a -4 initiative and loses 1/2 it's fly speed.  This stacks with the penalty for being overweight ( so a fly speed of 40 becomes only 10 when carrying double in a building that is too small).   It can not fly at all in a building designed for small creatures (5x5)

If you are Medium sized, then your mount is Large and needs a Huge (40 ft x 40ft ) for no penalties.  In a  Large (20x20) room it has penalties, and it can not fly in a building that is 10x10.

You can fly through a window that is technically one size too small to fly through, by spending an action and making a successful acrobatics check, DC 14.  I.e. A human (M)  riding an giant owl (L)  can fly through a 10x10 sized window on a DC 14.  But if the window turns out to be a 10x10 corridor, the creature lands immediately.  It can not fly through a window smaller than 10 ft.  If there are glass panes in the window, both you and your mount make a Dex check of DC 16 negates or take 2d6 glass damage.  

If you fall unconscious or are knocked 'prone' while flying, then the mount (if unaffected) can make a Dex check DC 14 to catch you.  If the mount becomes restrained or otherwise incapacitated, you begin to fall.  Hopefully you have a spell slot available for Feather Fall.

 

Once you achieve level 10, you can pick from certain more powerful mounts, assuming you can find one and befriend it.

Quetzalcoatlus

Quetzalcoatlus are Huge sized Dinosaurs, they make good mounts for Large Sized Aviators.

Eagle

Eagles are Small sized mounts, good for any Tiny sized Aviator.  Most often found being ridden  by Tiny Fey, such as Quicklings.

Giant Bat

A Giant Bat is a large sized flying creature, suitable for Medium sized Aviators.

Giant Fly

Giant Fly is a large sized mount suitable for any medium sized aviator.

Giant Owl

Giant Owl are Large sized mounts, perfect for a Medium sized Aviator.

Griffon

Griffons are Large sized Mounts, suitable only for an experienced (level 10 character level) Aviator.

Pegasus

Pegasus Mount is a large horse with wings. It is capable of carrying a Medium sized Aviator.  Being a Celestial creature, they only accept Chaotic Good or Neutral Good Aviators, and you must be at least 10th level.

Pteranodon

Pteranodon are Medium sized flying Dinosaurs.  They are a great mount for any Small sized Aviator.

Reduce

At 7th level you gain the ability to Reduce you and your mount one size, using an action.  When reduced you have disadvantage on strength checks and strength saving throws, all movement speeds are reduced by 10 ft, and weapons do 1d4 less damage.  On the plus size you can fit inside most buildings while reduced.  In addition Stealth checks have advantage while reduced.  This reduction is magical and can be dispelled.  It lasts for 1 hour but you can extend that time by using the same action (without having to enlarge). 

Most importantly, you can end the reduction at any time using a bonus action. If you are in a space large enough for you to fight in at full size, but happen to be reduced, you can time your bonus action size increase to take effect during your attack action.   When you do this, you gain a bonus of +5 to hit and +5 to damage for your first attack.  This works with any single non-spell  attack - those of your mount or by you - even ranged attacks.

You can use this ability unlimited times - but it takes an action to reduce your self again, so you are effectively giving up all your attacks in one round to get +5 to attack and +5 to damage for a single attack.  Most of the time it is only worthwhile if you reduce before the battle begins.

Grooming

At 11th level you and your mount both gain the Second Wind ability, but affecting each other.   When you use this ability on your mount, it is healed 1d10 +  your ranger level  hitpoints.  Similar, your mount can heal you the same amount by licking you.   In either case it takes a bonus action to heal (by you to heal your mount or your mount to heal you).   You have to tell your mount to heal you (via a bonus action), unless you are unconscious, then it uses it automatically.

This ability is usable once until you do a short or long rest before you can use it again.

 

 

Strong Mount

Once you reach 15th level, your mount has increased in strength and power.  It's fly speed increases by 10 ft and the first attack you (or your mount) take after diving at least 10 ft down does an extra 1d6.     In addition, all carrying amounts are doubled.