Ash's Naganadel vs Gladion's Silvally (can use RKS)
Ash's Naganadel vs Ash's Melmetal
Tapu Koko (no Z-move) vs Gladion's Silvally (can use RKS)
Tapu Koko (no Z-move) vs Ash's Melmetal
Gladion's Silvally (can use RKS) vs Kukui's Incineroar (a) with and b) without Z-moves)
Tapu Koko (no Z-move) vs Kukui's Incineroar (with Z-moves)
Ash's SM Pikachu (can use Z-move but not 10kkVT) vs Kukui's Incineroar (a) with and b) without Z-moves)
Naganadel vs Silvally could go either way, although I'm leaning more towards Silvally due to its superior experience in battling, but if Naganadel gets more time to battle and hone its skills, then it definitely can beat him given it threw down with Tapu Koko for a little.
Naganadel vs Melmetal would be pretty interesting, but I'd be leaning more towards Naganadel thanks to its superior speed, range and mobility, while Melmetal is mostly pretty slow and would have a hard time hitting him, but if Melmetal can take him down from the sky, then he can definitely win.
Tapu Koko, no question there. Silvally definitely has a lot of potential and I could see it facing Tapu Koko and giving it trouble, but not winning since it's basically Naganadel on steroids, which would already be enough to give him some trouble.
Tapu Koko is, once again, Naganadel on steroids, so he takes Melmetal down.
Incineroar is definitely above Melmetal, and I could see it giving Pikachu a lot of trouble, so it definitely would be capable of facing Silvally and beat it, not only does it have way more experience, but with or without z-move is strong enough to beat it.
Pikachu definitely was ahead of Ash's entire Alola team in terms of power output, with or without Z-Move, so I could see him taking down Incineroar if both could use Z-Moves, but he would lose if Incineroar could use but he couldn't for sure.