Marian - Riptide

Marian - Riptide is not currently available as a Trial Operative in any story mission, so if you don't have her the only way to try her is to wait for her banner so she has a trial.

Riptide is a Chaos Damage Skill Sub-DPS who provides Skill DMG buffs to the team.
Riptide does deal good damage, and the Skill DMG buffs make her quite easy to fit alongside most skill dps charaters, although Riptide does want to swap in quite often, which can be a problem for some dps-ers, although being one of the games few pure-skill dmg buffers Riptide is a popular support for skill dmg characters.

The Basics

Role: Sub-DPS
Chaos Damage
Deals entirely skill damage
Mobility is about standard

Advantages

Very high dps if used properly
Strong skill dmg buffs
Very easy to use

Disadvantages

Very poor as a main dps
Doesn't work as well with characters that have very long-duration skills
Very little time spent on the field means purchased outfits aren't necessarily good value

How to use Marian - Riptide

1. Use your Main-DPS
2. When your Main-DPS has used skills enough for Marian to have gotten 4 Kraken rounds swap Riptide in via her support skill
3. Magdump
4. Swap your main dps back in
Repeat

Standard Attack
Just a standard shotgun shot.
You'll never use Riptide's regular attack though.

Standard Skill
Marian loads 1 Kraken round into her shotgun.
Kraken rounds have basically infinite range, have a very wide hitbox (making aiming quite easy), and do vastly higher damage.
(With enough investment potentially over 10x the damage of a regular shotgun round.)

Note that Kraken Rounds count as skill dmg, not shooting.

Ultimate Skill
Riptide basically throws what is effectively a grenade in front of her to deal AoE Chaos damage.

Riptide's ult is very weak, and you're better off using the U-Energy for your other squad members.

Support Skill
If Riptide is off-field then whenever a standard skill is used [by any operative] Riptide gains Tidesong - charge for her Kraken mag.
Riptide gains 3 Tideside per second and an extra 7 Tidesong per standard skill usage. Each Kraken round needs 25 Tidesong, for 100 Tidesong for a full mag.

Once Riptide has accumulated enough Tidesong to have at least one Kraken round, you can use her Support Skill to swap Marain in.
When swapped in, Riptide will have her Kraken mag loaded and ready to go, so you can just instantly click to start magdumping all her Kraken rounds.

Riptide is best played as a sub-DPS, waiting until her Tidesong is maxed and she has 4 Kraken rounds, swapping in to shoot all her Kraken rounds, then leaving the field to let her Tidesong recharge.

Note that Tidesong counts as a special magazine, and hence can't be used alongside the special mags from Fenny - Starshine.
Note further that her Special Skill loads the Kraken Magazine from her Standard Skill, so if you see some of Riptide's buffs say they buff her standard skill that's why - it's because her support skill is an extension of her standard skill.

Weapons

Abyssal Nymph
Her 5*, and her best weapon, giving her lots of Skill DMG and Chaos ResPen.
Opal Prism
Her signature 4*, which gives her a sizable Skill DMG boost.

For Weapon Parts just go max ATK.

Logistics

Use Aileron squad - it was designed specifically for her and is her best choice.
Note that when Aileron was first launched, it worked with any operative, allowing other characters to give the entire team the +30% Skill DMG.
This has long since been patched and Aileron now only works with Riptide.

For stats you want +10.0% ATK and +106 Alignment Index.
For the Special talent, you want 8.5% Chaos Damage

Just max damage, basically.
Alignment Index gives the entire squad a Standard Skill DMG boost, which is great.

As a skill-dps, crit mods are useless to Marian.
Her Tidesong isn't affected by S/U-Energy regen, so those are useless.

Manifestation

M1increases the RoF of her Kraken Mag, allowing for more shorter rotations and thus more damage.
It also gives a 10% Final DMG boost to Kraken Shells, which is very nice.
M2 with the entire squad a 20% Skill DMG bonus for 8s whenever the number of Kraken Shells Riptide has changes.
If using Riptide properly as a Sub-DPS this is basically a permanent 20% Skill DMG bonus for the entire team, which is very nice.
M3 gives Riptide +20% Tidesong Acquisition Rate if equipped with a Chaos weapon (i.e. hopefully always).
Like M1, this allows for more shorter rotations and thus more damage.
M4 just gives her Kraken Shells more damage, which is very nice.
M5 gives Kraken Shells 20% DEFpen if Riptide is equipped with a Chaos weapon (i.e. hopefully always), which is a nice damage buff.

If you want efficiency, then M3 is a good stopping point.

Good Teammates for Riptide

Riptide's Skill DMG buffs mean that she works well with basically any character that deals lots of Skill DMG:
Crimson Moon, Styx Envoy, Tempest, Dawnwing, Jade Arc, Hush, Enigma...
If an operative deals mostly skill DMG, then Riptide will work well with them.

Riptide's M2 Skill DMG buff only lasting 8s means that she can be tricky to fit into the rotations of certain characters (notably Hush) however she will work and is still good regardless of how good her synergy is with the main-dps' rotation.

A few notes:

Riptide deals Chaos damage.
This means that if you are also using Celestial Swan alongside Riptide then you will want your main DPS to deal Chaos damage, otherwise Celestial Swans performance will drop significantly.
Styx Envoy really really wants Riptide on her team - Styx Envoy was designed around having Riptide as her Sub-DPS, and Styx Envoy performs much worse if she doesn't have Riptide.
I recommend you don't play Styx Envoy unless you also have Riptide.
The very long duration of Hush' ults means that Riptide's M2 bonus won't affect the latter parts of Hush' ults, which are the most damaging parts.
Riptide is thus not the best support for Hush. Still good, but there are better options.