Villain is 13/8 over 25 hands. No real reads, not sure if he's a reg or anything but he seems pretty tight. Not querying what to do with my actual hand, more just looking at how to construct a river bluffing range.

Seems very straightforward so far. I put villain on a fairly pair-heavy range, I imagine they would 3-bet most Ax hands here that they're VPIPing with.

Obviously if villain's range is pair-heavy then this is a flop they're not going to call very much. Once they do call I figure it's not a great spot for future aggression since their range is heavy on Ax/Qx and mine is wide.

Pretty much giving up on the pot here. Villain has some flushes now (although not many), and will have some KQ etc that contains a spade and therefore will not fold here as often.

This is where the idea of bluffing starts to be interesting. Qs blocks a lot of villain's flushes (QsJs, KsQs), and since it's hard for them to have AxKs or KsJs (would have either 3-bet preflop or check-raised flop some %), they're a little bit capped at AxJs here in terms of flushes. They also can't have many FH combos either - AQ or QT would have check-raised the flop some %.

We can't really have many FH combos here ourselves since we would have bet turn with 2 pair or a set, so my question is, would we be value-raising the Ks on the river? If so, which hands are the best bluffs to balance? We have all combos of KsQx/KsKx/KsTx in our range, plus maybe even Ks5x, but I can't figure out how to choose a bluffing range. I guess we need blockers to his bet/call range on the river, so maybe something that blocks the combos of hands that have the Ks, but I can't even find many combos in his range that have the Ks. Perhaps a T blocker to block QT? I'm a little stumped. Maybe someone can help me out.