Heres a little feature piece on one of my most liked support pokemon, it is rather unique as it has convenient immunities and resistances as well as a move pool that sets it apart from other support/tank pokemon such as Cresselia and Gastrodon.
Pros & Cons
+Great support move pool
+Anti weather immunities
+Easy to partner with
-Poor offensive presence
-x4 electric weakness
Mantine is unique in that it conveniently is immune to both earthquake and surf, making it not only a great support for pokemon who enjoy using these moves but also a great check and counter to sand and rain teams respectively! The major difference between Smogon doubles and VGC is 6v6 as opposed to 4v4 and as such, with longer games, the support Mantine gives is incredibly difficult to match!
Mantine has a support move pool that is hardly lacking, I'll list a few important moves below:
Wide guard is the most important one as it can really help against the discharges and rock slides that plague Mantine whilst your partner attacks. Helping hand is fantastic in doubles and icy wind and tailwind support is great for speed control. Mantine also makes a great leftovers holder as it will be very rare for it to last less than a few turns assuming you take care of it and avoid electric attacks or too many rock slides.
Heres a sample set:
Mantine @ Leftovers/Wacan Berry
Trait: Water Absorb
252 Hp / 252+ Def / 4 SpDef
I used this on my hail team to great success, it deals with all weathers. Wide guard is a great support and perhaps the main reason you would choose Mantine over other support mons. Defence is maxed with a positive nature to give Mantine a better chance at surviving rock slides and toxic removes common walls and deals with multiple "bulky" pokemon that care little for icy wind. Helping hand allows Mantine to do something when offence is required and makes it a great partner for pokemon such as Volcarona that can really use a 50% boost. The best partners are either surf spammers that enjoy the helping hand or icy wind support as they heal Mantine or pokemon that could really use the wide guard support in order to set-up.
Mantine conveniently resists some of the most common physical moves in a specially dominated metagame (Fighting, Steel, Bug are all common) whilst taking paltry damage from any non-electric special attacks. The list of pokemon walled by Mantine, just from the top 10 is rather high! I'll list some of the most common pokemon Mantine walls rather effortlessly. All of the below are top 20!
# 8Latios (without thunderbolt and with surf support to keep Mantine healthy)
It can also hold its own against Terrakion/Tyranitar/Garchomp/Excadrill/Landorus-T as wide guard can give it temporary immunity to rock slide whilst your partner attacks leaving only Ferrothorn, Dragonite, Whimsicott and Rotom-W as top 20 pokemon that can give it consistent trouble!!