Preparing for Prisma Causeway

Let's see...I suggest levelling Tamamo lancer to at least 60 or 70 if you could since we're going to fight Chloe I heard so an ST lancer would help. Assassins aren't going to help much and Medusa is quick which the event doesn't give a boost to, so level her on second priority just to help if you have spare time and then start farming Camelot to the ends to make mash stronger since she might save you. Also save some embers for Chloe since she'll be your main damage dealer with the lack of female servants
And If I were you I'd start hunting a leveled Mebd since she's be useful for the event or a drake if you can.

Farm for embers and raise your Tamamo. She's your best female servant with a buster deck to take advantage of the damage bonus. You'll also want a female rider to help you farm but you could always borrow a friends Drake instead if you won't have the time to raise Tamamo and a rider. You can still use Male servants, they just won't get the 50% damage boost but will still have class advantage

If you need some help from a friends list, here is what I’ll be using as my support list for the event. Gonna spend the 1/2AP week boosting their skills as much as I can. If you think they can help you, let me know you sent a friend request and I’ll accept. 825,960,988

Already boosted Nightengale’s skills to 5/4/5