Hmm... that was a rather painful round... Reflect seems much less effective than Swords Dance. But anywho, Celeste, don't give up just yet. Let that thing whip up the sand, then start a Rain Dance to cancel that out, and I'm sure a ground type won't like the rain either. Then use a Teleport to dodge that incoming sludge, and follow that up by hitting her with Ice Punch. Get some revenge for that 4x weakness against Equinox.

Rain Dance ~ Teleport ~ Ice Punch