LEGENDS HOW DO THEY WORK

Supernatural Gifts:
Whether someone is just arbitrarily Touched or Blessed by a legendary Pokemon, or whether they've actively sought out its service, these are the supernatural powers that they gain from the process. Intent and process are irrelevant to the actual mechanics - the powers they end up with will be the same for the sake of simplicity and not having to make different blessings for someone serving a particular legendary as a god and someone merely Touched by them.

They'd be split into two categories, one as a prerequisite to the other:

Minor Gift: This would take the form of an Edge and is often not overtly supernatural at all. It may come in the form of a minor boost to particular rolls (ex: Uxie could allow their Blessed to reroll all 1s when making Knowledge checks),

Major Gift: This would take the form of a Feature and often is both overtly supernatural and quite impressive - oftentimes, this takes the form of granting the trainer Moves, Abilities, Capabilities, or some combination thereof. Victini may gift a trainer with the Victory Star ability. Groudon or Kyogre may grant them Drought or Drizzle respectively, Meloetta may grant a trainer Relic Song, Shaymin may grant Sprouter, and then there might be other more feat-like ones like Cresselia granting the ability to see into others' dreams, or Giratina allowing the creation of portals going through its realm for travel.

Pact Gift: This is a major effect, such as learning a powerful move. Trainers may only have one Pact Gift. No matter how many legendaries they manage to befriend.

Tribal Rituals:
These are accessible only to those who are actively honoring a patron legendary, and they are Feats that allow the user to perform minor miracles.

Generically speaking, these may be cleansing food, detecting Pokemon around them of a certain type, etc.

Signer Bullshit:

Yeah fuck if I know how to handle this right now, but here goes

Signs have a mechanic for charging them up - either doing things devoted to the legendary or...I dunno, something else.

Signs have a small active effect that can be drawn upon for an amount of charge - for Raikou/Entei/Suicune this may be improved jump for one action. Generally, I see these as being "field" effects, things that aid a Ranger in traversing harsh environments, rather than something on the more mental side of things.

They also have a greater passive effect at a certain threshold of charge - such as granting Pressure to the trainer or something else that would generally be a passive in-battle benefit. This may overlap a bit with Major Gifts.

At max charge they can spend all their charge to summon a phantom of a legendary. This would last something like three turns before disappearing, and requires command actions to use as normal.

I imagine as far as mechanical structure goes, a Signer takes one feat that grants them the small active effect as well as the ability to gain the greater passive effect at a level of charge. And then a second feat that allows summoning a phantom of a legendary.