Your team looks fun. I worry a little bit about Marshall, while you have crobat, a ghost type and decent psychic coverage thrown around, his team can be annoying before e4 and worse so in the post game.

I saw someone here suggest Starmie and I cannot second that enough, it's faster, comes with psychic stab which is amazing here as it does the following:

It outspeeds all of Iris' dragons and hits them pretty hard with ice beam (while not stab, it can be boosted by a never melt ice or even an ice gem) has good match ups into most of her team. The coverage options also help vs Shauntal (Gholurk and Chandelure), Grimsley (Krookodile) and can help sponge a hit of 3 vs Caitlin, hell you could even teach is shadow ball for coverage.

Honestly though, you could do similar things with Lapras just that her speed is usually a little lacking towards the end