At first an alicorn differs little to a unicorn outwardly as they start on their ascension, during ascension there are milestones called summits. An alicorn reaches these summits every two levels in what order they reach these summits is random.

Roll 8d8 to determine in which order you gain a summit.

1. Mane: the alicorn's mane and tail waft on an invisible and intangible wind and take on the aspect of the alicorn.
2. Horn: the horn lengthens and becomes more potent as a foci.
3. Wings: a pair of wings appear on the alicorns back. Allowing flight using a bonus action the alicorn can take off or land if they are already flying.
4. Alicorn sight: the ability to see magic and the weave as well as the wellspring of living beings even through solid matter, and the ability to see a dark tar like substance called miasma which stains where people have died.
5. Animal speech: the ability to speak to animals and understand them.
6. Gem finding: the ability to locate gems.
7. The instinct: ponies and other equines instinctually follow the alicorn and become subservient when in close proximity.
8. Alicorn height: the alicorn becomes 6ft in height this happens gradually.

The instinct felt by every alicorn to protect ponies and other equines, others that do harm to equines. Even if they maybe equines themselves gets the focus of the unrivalled ire of the alicorn. The alicorn must roll a 1d20 wisdom check anything lower than 10 results in the alicorn going berserk anything above 10 the alicorn succesfully reigns in their rage.

When an alicorn goes berserk they will give off an aura of their aspect, they cannot target any other target except for the one that triggered their ire until that target is reduced to 0 all damage against the target is doubled. A party member can try and reason with the alicorn to break them out if it. To do so the party member must make a charisma check against 10+ the alicorn's level. Regardless of which way the berserk state ends the alicorn cannot take a full action. Only movement and a bonus action.

At level 10 due to the earth pony magic in an alicorns body they regenerate hp and lost limbs at an exceptional rate.

Per turn you can roll your Hit die＋Constitution Modifier to heal yourself. Your able to use your Hit Die to prevent your HP dropping past 0, and avoiding death saving throws. Once your HP drops below 1; Instead of Rolling for Death Saves on your next turn. You roll Your Hit Die instead to Add to your HP.

At the end of each turn a single limb is restored, the lost limb a turn after it was removed from the alicorn violently burns up damaging any creature within 5ft sphere from it for 1d4+int modifier of fire damage.

Unlike the other horn less members of its equine kin the alicorn can use its magic as it's hands through telekinesis. As such checks that require strength  (lifting, pushing, pulling) use intellgence instead of strength and those requiring dex (aiming, lock picking) require wisdom. Further melee weapons double their range and for every 5 points to int the alicorn can equip an additional melee weapon.

Prerequisite: gem finding summit

The alicorn gains the ability to detect nearby gems once per long rest, roll 1d20 to determine how many gems and 1d500 to determine each gems value.

The gems must be dug up first DC is determined by dm as appropriate.

Prerequisite: magic sight summit

Once per short or long rest as a reaction you can use your magic sight to copy a spell being cast so long as you have spell slots of the appropriate spell level.

The aspect is how you effect your surroundings and what your mane and tail look like.

these aspects include: 

Roll a 1d14

1. The sun
2. The moon
3. Magic
4. Water
5. Earth
6. Fire
7. Ice
8. Lightning 
9. Wind
10. Stars
11. Illussion 
12. The weather 
13. Nature
14. Gravity

if you are reduced to - your max hp for example you have 10hp you get hit with 20 damage you die. on death. the players have a round before your body violently self immolates for 1d20+your max hp fire damage within 10ft sphere from your corpse.  

Earth Pony
at 1st level the Alicorn gains the Stamina, strength and self healing of an earth pony. +1 to Strength and Con

at 5th level the Alicorn gains the ability to create a localised Earth Quake  knocking every creature who fails a dc 15 Dex save once per short rest

at 10th level the Alicorn can heal another creature using it's hit die once per long rest

Pegasi
at 1st level the Alicorn gains Weather control, Cloud walking and manipulation,

at 5th Level improved vision wisdom and dex +1
half damage from fire, cold and lightning alongside a exceedingly soft coat.

Unicorn
At 1st level the Alicorn gains Magic, keen mind. +1 to intelligence

at 5th level the Alicorn gains the ability to use metamagic feats choose one meta magic feat from the sorcerer

10th level the Alicorn can use alicorn magic a melding of the three tribes magic to create pseudo 10th level magic. (9th level spells with the power of a 10th level)

The alicorns are not gods and to worship one is to cause it to eventually go insane.