Supporting is a really strong playstyle in team-play and used mostly for Road or special custom quests like multi musou hunts. Your job as a support is to heal your teammates when they get hit AND paralyze the monster for some crowd control. Certain monsters will struggle to kill hunters with a good support, since a hunter can only faint once he touches the ground. That means if you die mid air you can still be healed and survive a lot of combos.
As a healer you should be playing more careful than normal and be ready to heal when the monster does a dangerous attack. There's nothing more frustrating than getting hit yourself and therefore being unable to safe a teammate from fainting. You will need to know what attacks are dangerous and be ready to avoid them to do this effectively.
The main loop for applying status is Adv. slash -> evade-slash -> repeat. This also gives you hyperarmor to not get staggered by teammates.
Anti-Venoms can be given to the entire party if you have Wide Area+3, this gives Zenith poison immunity and a 50% damage reduction for the entire team.
I recommend two support sets.
The first is a general set that you will use most of the time and allows you to do everything a support needs to do and do good damage without losing too many comfort skills.
The second set is a pure healbot set that does absolutely no damage but makes you almost unkillable and uninterruptible while supporting your team.
I personally only use the Heal Bot set on extreme challenge quests like EX road, apex bounties, multi musou Hunts, etc.
To understand the Heal Bot set a bit more be sure to read through the skills it uses:
Absolute Defense will fully nullify an attack with an ever increasing cooldown when it gets used. Be careful with this since you cannot PD while the shield is up.
Imperturbable will make you not interruptible when taking potions/anti-venoms, and with Guts making you immune to oneshots you should never struggle to survive and keep your team alive.
Herbal Science not only lets you heal teammates with G2 Potions, Max Potions and Quick Max Potions giving you 16+ more heals, it also buffs your healing items according to how many people run the skill in your team. Do note this requires at least one other person running the skill (you can Guild Food for it).
You can let your sharpness drop to red to get rid of hitlag. This will make you build up para faster but can be awkward to play at first.
The only real weapon choice you have is our beloved Divine Galatine. If you want a cheaper option you can use a paralysis tower weapon, but be sure to put SSU on it. The tower weapon will be worse in both status buildup and damage though so getting Galatine should be one of your top priorities.
For the sigils I recommend to at least get the Beamslash and unsheathed walk/status effects, The z-AOE sigil is also really good if you coordinate with your team. (for the Unsheathed Walk Sigil roll the Guanzorumu ★ sigil)
Ideal Sigils:
Beam Slash | Length | Status
Z-AoE: Stun | Status | Attack+15
Unsheathed Walk | Status Attack | Stun Value
I usually start by buying:
10 Mega Potions
2 Whetstones
2 Steaks
10 small barrel bombs.
From there try to save up for an Elixir of Peace asap, but always prioritize items like Bleed Cure's, Flash Bombs or even Ice crystals, if you need them.
You can exchange the Fruit for whatever you need in the moment.
Flashing Z-Espinas guarantees an anti-venom per flash, do this as much as you can if you need anti-venoms.
Use the shield bash infinite combo in a corner while not in the arena to build furious for teammates.
Flash Farunokku at the start so he doesn't run over your team
Flash Stygian right after his enrage to delay his nuke
Flash Chameleos at the start to delay his nuke
PD small barrel bombs to build your own furious
You can buy Ice Crystals in the shop and if you use them during transcend you can build up an Ice Hexaflash for a long lasting freeze on the monster.
Important Monster CC Chains, this assumes at least 1 MS in your team to pin and consistent sources of KO damage such as Hammer, more MS, impact SAF or even tonfas.
Fatalis: Para -> Pin (place your Z-AOE sigil here) -> Para, he should die after this.
Z Doragyurosu: Stay at spawn and place the Z-AOE sigil, roll through his dive and you should get a KO. Instantly after the ko Pin -> second KO. He should die after this.
Z Plesioth: From spawn walk backwards to the wall and place your sigil, help your team to get the initial ko. Don't overdo it with your hits to not para it too early. MS should pin then you can finish the Para. Hope that it's dead after this.
Z Baruragaru: Walk slightly forward from spawn and place your sigil. from there its KO -> Pin -> KO -> Pin and so on.
Most Zeniths have a guaranteed CC rotation like this, but its often required to improvise on the spot. Just try to estimate your para and ko thresholds to not cancel each other out.
If you want to complete the EX Road f150 bounty it is essential for your team to be very consistent. The damage scaling on the Musou Monsters really changes the fight to a surprising degree so not getting hit becomes necessary past f50. I'll try to explain the strategies I used on each Musou to finally make it after a lot of attempts.
Zeru: After he lands you can CC him for a very long time. The rotation I found to be most useful is:
KO -> Para (use Z-AOE sigil here) -> KO -> Para -> Ice Hexa -> ???, this will not always be consistent but it should be relatively easy to CC him until he flies away again. After that if your team can't get KOs be sure to play extremely cautious and use AV's until he dies.
Deviljho's: As the support you should run away and keep using AVs. Be sure to bring the maximum amount of healing possible as well as using transcend to heal. This shouldn't be a hard fight but its very heavy on resources. Don't forget random balls.
Boga: A very easy fight for you, but not your teammates. Past f50 AV doesn't protect from oneshots anymore so your teamates have to be very careful. Your job is to get Paralysis asap and follow it up with an Ice Hexaflash. With the Healbot set you can safely play aggressive and give your team a breather with the easy CC. If you have a hammer on your team or the MSs decide to play blunt mode you'll also get frequent KO's. Nonetheless this will be an endurance fight lasting a long time and a single mistake will cost a live.
Zino: My usual strategy was just to run away and hide. From there observe your team and heal them if they get hit, and be sure to use AV constantly. In my experience it's too dangerous to stay close and will just cause either you to die or not being able to save people.
Narga: Fun but dangerous. Fight with your team to not cause narga to nuke randomly. Use AV/Potions whenever you get an opening and never while narga's attacking. In this fight you can't rely on imperturbable because of the many multihits he has, so just playing a clean narga is key. Use Ice Hexa right after your first para.
I'm not gonna explain Elze since he should NEVER be picked if you're goal is a high floor.