I got bored of moonstone seraphine so I decided to create this guide. This is for damage but still has utility with your e insta-rooting people and you still having good shields. I'm just a casual Seraphine player who goes by "miss girl" on OCE. I am however m7 on her regardless of not being the biggest onetrick.
So if you're looking for a different way to build Sera in support this is the guide for you.

My op.gg: https://oce.op.gg/summoner/userName=miss%20girl

She is a very fun mage to play in support and i feel she has a lot to offer a team if played properly. She can also be like a pseudo-enchanter for her team with staff and ardent. Seraphine has fewer weaknesses than other enchanters or mages like her with aoe cc like stuns and charms.

With seraphines Q you want to be minimising the use of double Q until you get mandate + ryalis as with ryalis your aoe q applies mandate which can give your team a lot of extra damage. Also be careful with your mana costs pre bandleglass mirror

In lane save this for clutch saves on your adc or if trying to retreat from a gank. If you or your adc is going to take a chunk of damage like a jinx w etc use this ability. Late game try to get as many people in the radius before you double cast for increased shield.

With your e make sure you are using this the most to proc mandate before you get ryalis which makes it apply on your Q as well and makes your e insta-root.

Be careful with using this ult too early, wait for the engage to happen with their team going in on you or yours going in on them. If some initial cc lands before then they can't avoid the damage and charm from your ulti. This makes it much more easy to land and leads to a basically insta won teamfight if it connects with over 3 members. The cooldown is very long compared to some ultimates so be careful.

Try to make sure you're in the middle of your team with as many passive notes being procced as possible. If you're in the middle of your team and double cast W then your team will have a massive shield and heal just from being near each other. With this build you want to be trying to apply mandate on as many people as possible so your team can proc it. This leads to a damage boost for your team and you get to move a little faster because of mandate passive.

Although this build used to work better with pre-nerf mandate I feel as though it is still very strong and better than moonstone in many situations after the moonstone changes. Sera is meta ty