Well, 999kirby pretty much covered it already, but here is my version.

Abilities and mechanics:

First wave, 40m HP, 6 orbs.
Huge elemental resistance to all but Light and Thunder.
Immune to movement stopping debuffs (Charm, Para, Flame Bind)(Nutaku has translated this as "immune to everything", thanks Nutaku!). BP works.
Overdrive: Deal 10 000 fixed damage (damage cuts do not work against fixed damage!) + give 10x Overdrive attack buff to self (cannot be Dispelled)

Trigger: when taking Burst Streak damage: max out orbs (OD is probably priority)
Trigger: 50% HP: full Cleanse and Dispel to everyone (self and party)

Second wave, 90m HP, 4 orbs.
Huge elemental resistance to all but Light and Thunder.
Immune to movement stopping debuffs (Charm, Para, Flame Bind)(Nutaku has translated this as "immune to everything", thanks Nutaku!). Additionally, BP does NOT work.
Normal Overdrive: AoE ~15k damage + -50 Burst
Rage Overdrive: AoE ~15k damage + -50 Burst, then single target ~15k damage + -50 Burst

Trigger: 90% HP: Self buff which prevents combo attacks (does not expire, does not eat Orbs if full, cannot be Dispelled?)
Trigger: 50% HP: Self buff which prevents combo attacks (does not expire, does not eat Orbs if full, cannot be Dispelled?)(this is a completely wasted turn it seems like)
Trigger: 30% HP: full Cleanse and Dispel to everyone (self and party) + become immune to debuffs (does not expire, does not eat Orbs if full, cannot be Dispelled)

Normal attacks:
Above 30% HP, when not holding debuff Prevention: ~4k single target + self debuff Prevention (once)(cannot be Dispelled)(ODs take priority)
Above 30% HP, when holding debuff Prevention: 2x 10k single target
Below 30% HP: 10k single target + Dispel
(according to DMM wiki, below 30% attack will be used even during Stun - unless Orbs are maxed)

Some words on how to fight:

Bring debuffs. I know right, more content where debuffs actually matter! Def- and Atk- are a godsend until the very end.

The first fight is a simple turtle denial fight. Which is pretty dumb. Without BP or Orb Eats, you have ~13 turns before you simply die. But at least it has "only" 40m HP, which also means that after 20m HP it will eat away your debuffs. That happens probably after your first burst, so keep that in mind. And remember not to burst until it has full orbs!

The second fight is the problem. Hopefully you can pace yourself and get into the fight with all your abilities up. While Python only has 90m (which is rather low for a Heroic final round), it's a complete bitch to fight. Because you can only single attack, burst generation is extremely low. In addition, ODs eat 50 Burst from everyone which means that typically you cannot Burst ever. There are ways around this - skills that generate Burst and Orb Eats. Combine both and you can Full Burst just fine. Just be mindful of pacing - if you burst from 50% to 30%, you're probably pretty fucked since the last 30% is the hard part of the fight.

Additionally, if you don't want to get single-target nuked to oblivion, you will need to use one debuff every single turn during the first 70%. Notice that while BP doesn't work against Python, you can still use it to remove the debuff Prevention. Anyway, your primary means of removing debuffs are Eidolons. Bring as many Eidolons with debuffs as you can and you should be fine assuming that your party has a few extra of their own.

The final 30% (~27m HP) is a simple damage race. One of you is going to die and there isn't much you can do about it. According to DMM wiki, Southern Star Lord ignores the entire "immune to combo attacks" thing, and obviously Northern Star Lord is extremely good as well. If you have either, this fight will be SIGNIFICANTLY easier.

My personal experience and opinions on the fight:

I have no idea could my Light handle this, but thankfully, I don't need to find out. Went in with Thunder, fucked up my pacing by bursting from ~50% to ~30%, became a fairly close fight but Dian potions saved the day.

Hopefully this whole "two elements work" thing will become a thing (and to my understanding it will). This significantly reduces the chances of you just getting fucked out of content simply because Gacha has decided that "THOU SHALT NEVER FIND x ELEMENT"

I don't understand why the devs hate turtle teams so much. If somebody wants to suffer through some 130m+ HP by turtling, let them? It's not like that's hurting anyone. Aside from that, I think it's a fairly decent fight. There are many, many different team comps that you can make, like bringing Yori to FB your way out of the final phase, though that will make everything before it much harder. You can bring Medea, as skill damage will work just fine when you can't rely on normal attacks or bursts. You can bring Perseus for tons-o-debuffs to deal with the debuff Prevention (and his guaranteed Orb Eat MEX to reduce ODs), or maybe bring a single-target Guard hero like Athena to just soak up those hits. You can bring a defensive team with Romulus and just soak up the hits and slowly five-punch-per-turn your way through the fight. I always like it when there are lots of choices for clear content, because what you should do will largely depend on what you will have. Oh, and bonus points for largely disabling both of our new saviors Paras and Parac with the combo-killing mechanic, so for once you won't be shoehorned into using either (though both will work to some extent).