I've gotten to the point where I get the writing on the wall but I don't always have the right sylesti up. I did one that I thought was supposed to be Agility but nothing happened... and the next one I didn't get because I didn't have the right Sylesti in my team. >< What do I do from here?

You can't see if the seal works unless you get all correct, and even so, you'll only know at the 4th seal.
here's a thread discussing the seals: https://www.sylestia.com/forums/?thread=622


If you encounter a seal that requires a different pet, you can always switch the right pet to your team, activate the seal, then switch back to your normal team.

And honestly, you don't need to activate all the seals to fight the boss. It'll just make the fight easier. But if you have a good team, you can still defeat the boss without activating all the seals. When i fought that boss, i only managed to activate 2 seals.

oops forgot to let you know I got through it with your help. Thank you. =^-^=

No worries. And you're welcome. ^^