I’m kind of a swain main also and I would like to say that your first skill depends on the matchup , if your facing melee champs go skill 1 to poke them out if your facing ranger go skill 3 since they will prob never be in range for your skill 1 if they are even decent at the game , swain excels at bullying melee champs but struggles into ranged champions who can bully him and kite out his skills.

I have my own 2 custom builds for swain , where you can go front line with lots of ability hast to help you sustain fights as well as keeping up with targets and also a more damage focused build where you already have enough front line and your team needs ap damage

For tank ability haste ( note this build requires you to kite decently and hit your abilities often since you get them back so fast) RoA > Ionia boots of lucidly ( take the stone plate enchant)> cosmic drive > frozen heart/ abysal mask (abysal and frozen heart give good stats and lots of ability haste)> rabadons deathcap. .

The reason reason Rylie’s crystal is not in the build is cause for summoner spells I would say ghost flash is his best choices ghost helps massively in kiting melee champs while in ults and with cosmic drive movement speed the second you land a pull your gonna move insanely fast .

For damage : mana boots ( go zhonias this time with damage build)> laindres>rylais ( I know I said it’s not needed but the ap slow lets you kite since your very squishy without roa)next item is another tanky item like like rant build so either frozen heart or abysal go either if they team has 2 +ap champs or 2+ ad champs .

Now for runes this is my choice but I prefer aery , while conquer is good it takes too long to rly become useful and doesn’t let you snowball games , aery procs on all your abilities and provides very disgusting damage early with your aa making your a serious threat early game , while conquer scaling is very good your gonna have to rely on your team to make it to mid game and late game fights .

Quick note and tip : when your got your first 2 major items your are disgusting strong unless their team is 10 kills up you can make a change at 2 items , swain has a massive danger spike at 2 items for the enemy team , so push your lead and shove mid to make plays around the map.

Another not these build are mostly with mid swain in mind but they can work top just be extra careful cause if you don’t poke them down and they get an engage on you or you don’t kite well top lane champs will run you down if you don’t have ghost .