Shadow Lapras

Even with the Shadow Boost, Lapras has not regained the glory that it once had at the start of Pokemon Go. As both an Ice Attacker and a Water Attacker, the added cost of its investment is not worth the performance that Shadow Lapras will give back.

Best PvE Offensive Moveset

• Frost Breath and Ice Shard* are both great go-to Ice-type options for offense.

• Water Gun should be paired with Hydro Pump, but is undesired, as Lapras’s niche is in its STAB Ice-type moves.

• Blizzard is on par with Ice Beam* on paper, but Ice Beam will pull ahead more often than not due to its higher average performance. Still, it's probably best to not drop an Elite TM on Lapras.

• Hydro Pump performs similarly to Surf, akin to the above Ice-type charge moves.

• Dragon Pulse* and Skull Bash are clearly the worst options due to lack of STAB and meaningful coverage.

Best PvE Defensive Moveset

• If you've got Elite Moves on Shadow Lapras, then go for Ice Shard* and Surf or Dragon Pulse
• If you're not packing Elite Moves, then Frost Breath is your go-to Fast Move, while Water Gun is... okay.
• Ice Beam* seems like it should be a great choice, but pairing it with Lapras' best Fast Move options leaves it easily walled out, and Water Gun isn't great.
• Blizzard, Hydro Pump, and Skull Bash all take too much energy to be useful, as Lapras will probably go down before using them.

Shard's energy generation makes it more important than Frost Breath's damage. Bummer that it's Legacy, though.

Surf is 100% mandatory on Lapras, providing very solid and consistent Water-type damage. Your secondary move of choice will depend on the format. Skull Bash is at its strongest in Great League and Ultra Premier, where you're likely to run into Pokémon that would resist a Water/Ice moveset (e.g. Azumarill, other Lapras). Ice Beam mostly sees play in the Open Ultra format, letting you really need that Ice-type nuke to hit Giratina.

What about Dragon Pulse?

Dragon Pulse was made a legacy move starting February 21, 2017, and now available through Elite TMs. Demanding 60 energy to use, it's slightly slower than Ice Beam, but does offer the perk of neutral damage against opponents that would resist Water or Ice-type attacks (AKA other Water-types). It's also handy in the Lapras mirror match, and easier to get to than Skull Bash, but does not offer a DEF self-buff.