I can't even begin to describe just how bad this Pokemon is. Just take a look at its stats, they're hardly better than Weedle's save for the Speed stat. That Speed does mean Luvdisc can nearly 100% guarantee Rain Dance or Safeguard being setup before bringing in Huntail, but that's not much a niche.
name: Rain Dance Support
move 1: Rain Dance
move 2: Safeguard
move 3: Surf
move 4: Toxic
ability: Swift Swim
evs: 252 HP / 4 SpA / 252 Spe
Your goal, or challenge, is to set up both Rain Dance and Safeguard before Luvdisc kicks the bucket (assuming your opponent will be nice enough to not just stall out the rain turns with Luvdisc still on the field). Surf and Toxic are so Luvdisc can try to be not completely useless outside of that role, but let's face it, it will be.
If your goal is to take Luvdisc on the offensive, your best bet is going to a Substitute + Flail set. Its Speed means it can almost guarantee it will get down to 1 HP, but even with a Liechi Berry boost its full-powered Flail isn't even a guaranteed OHKO against Roselia.
[Checks and Counters]
Luvdisc being on the field is your cue that your opponent is packing Huntail, so try to predict when your opponent will switch to Huntail and get your answer to it onto the field then. Just don't try to inflict your opponent with status if they have used Safeguard. As for Luvdisc itself, as long as it resists Water it can be considered a hard counter to it.