Im not sure i completely understand your choices here. I bet that a screen of your roster could help us to have a better sight and therefore give you a better advise
If you trap tools are limited and you can ascend only one purple id go with Tibs before then cyprian.
This is a personal opinion from someone who doesnt play with Riposte heroes, at least the classic pair from S1. They come so late to my roster than i never max them(i always had a better choice to pick)
However i can tell you that tiburtus will bring you def down that will improve your chances on events(teltoc) and against yellow titans . What is more tiburtus is a solid hero, if you manage to pull his costume you will have a hit to all def down user with overall solid stats(something like quintus with less damage , but faster and a better skill effect)
good luck
pd: I will consider a second proteus before cyprian too because i ponderer offensive more profitable overall than defense
No it doesn’t stack. You can spread it out. But Merlin-Proteus combo works better for raids. Because you can shut down one side and get the other side to hit themselves. Its really fun to watch.
But you should absolutely do Costume Rigard first. Then go for a hitter - Tiburtus. Then hope to pull his costume as well in a couple of weeks, and do Costume Tibs.
Btw, costumes cost lesser mats and level up faster.