Seraphine is a very flexible pick, and can be played as a supportive enchanter or a mid lane mage. Her powerful CC tools and wave clear make her a great pick in the mid lane, so let's break it down.
When playing Seraphine in the mid lane, it's important to remember that damage is not her primary strength. She offers a ton of value to a team comp, but is not like other mages who can blow up enemies or poke them down. Instead, Seraphine's strengths are her CC, versatility, and wave clear.
In the laning phase, focus on chipping away at the enemy as much as possible with your E and Q. It's unlikely her damage will be enough for a solo kill, so saving your passive + E when your jungler comes in for a gank is essential. Her W isn't very useful early on, but can be critical in escaping an enemy gank with the shield and movement speed.
The long range and AoE damage from her Q makes it a great pushing and wave clear tool, particularly when it's used with Seraphine's passive. Therefore, it should be maxed first.
Seraphine shines in team fights. Her ult is a fantastic engage or follow up tool, with its range being extended every time it hits an ally or enemy. Its relatively slow travel time means enemies can dodge it, but you can catch them off guard with an ult + flash combo. Ults can be followed up with an E for a dangerous CC chain.
Using your passive + W during team fights is extremely strong, as the heal scales with the amount of allies nearby. You can shield all of your allies, grant them movement speed, then heal them a few seconds later for incredible amounts as long as the team is grouped.
It's imperative you track you passive during the chaos of team fights, because utilising it effectively can determine the outcome. Even if there are no enemies nearby, you can use Q or E to prepare your passive for an upcoming fight.
Seraphine's build is very flexible. Liandry's Anguish is her best mythic, as it helps with her wave clear and is easy to proc given how much you can spam abilities. Tear is another essential item, ensuring you have the mana to cycle through your abilities and maximise your passive usage. This can be upgraded to Seraph's Embrace after your mythic, providing a ton of useful ability haste and some additional healing.
The rest of Seraphine's build is situational:
- Rylai's Crystal Scepter if you are ahead. This means your E will always root any enemies hit
- Zhonya's Hourglass if you're against a lot of assassins or AD threats
- Chemtech Putrifier if the enemy has a lot of healing. Seraphine can grant its healing reduction buff to all allies with her W
- Redemption if you fall behind. This provides a boost to your W heal and shield, as well as a powerful AoE heal
Summon Aery increases the poke damage from her Q and E, and can provide an additional shield from W. Seraphine's early game damage isn't high enough to justify taking Scorch, so the scaling from Gathering Storm is the better option.
Her secondary tree is a little more flexible. Magical Footwear is always a solid choice, though you can take Perfect Timing if you're going to be building Zhonya's. Biscuit Delivery increases Seraphine's mana pool further, but you can opt for Minion Dematerializer to augment her wave clear even more.
Although her early game isn't the strongest, Seraphine's excellent wave clear tools allows her to farm up and scale into the mid/late game. Once team fights have begun, she shines with her healing, shielding, and devastatingly powerful ultimate.