Quote from Chiyuri;1184688:
I think what the person want to know is how to party play as a magic user. If you play solo you usually take a mission you can solo on your own without having to care about anything else.. but for party play you usually pick an harder mission you wouldnt normally solo and some degree of team play is required
Party play doesn't really exist in Mabinogi anymore.
Your best bet is to coordinate your tactics in advance in order to minimize the butthurt which incurs after people realize that "party play" is actually just a bunch of people using solo tactics and getting in everyone else's way.
Hail Storm should be used when you have crisis support or find yourself in a situation where mobility is not a limiting factor and enemy spawns are relatively grouped, or otherwise sparse. Damage output is roughly 35~45k per critical hit.
Blaze should be used as a follow up to Ice Spear. The skill deals phenomenal damage to everything with a maxed down gauge but it's difficult to pull off reliably and it definitely requires a bit of preparation. When choosing between Hail Storm and Blaze as a follow up to Crisis ask yourself if you're running with any other decent mages. If the answer is yes, use Hail Storm. Damage output is roughly 45~65k per critical hit.
Fusion Bolt is best used to pick off stragglers or take down bulky enemies when you have time to prepare an attack. Fire/Ice Fusion Bolt deals upwards of 55~65k provided all attacks land critical hits.
Shockwave is an incredibly useful skill due to its large radius, average damage, and instant cast time. It's best used to shake groups of enemies off of your character or immediately following charge. Deals around 6~8k critical damage at point-blank range.
Fireball is not particularly useful in any situation where you cannot Snap Cast the skill. It's usefulness is limited; even Snap Cast double Fireballs are generally outclassed by Thunder. Deals around 25k critical damage.
Thunder is a fairly situational skill, though it shines in a few situations. Rafting, Falias, and NPC tournaments are all good examples of places where you should use Thunder. You'll want to attack with Snap Cast Thunder immediately after attacking with a pre-fully charged Thunder during the NPC tournament. This tactic tends to decimate up to around Round 5. It also has fantastic synergy with other mages in your team, allowing you to near effortlessly take down the tournament, provided you have enough mages (similar to Bullet Storm or Flame Burst parties). Deals around 25k critical damage, provided all attacks land critical hits.
Ice Spear is the best spell mages have at their disposal. If you can deal over 20k damage with a fully charged Ice Spear, tell anyone who cries about your use of the skill to shut the fuck up unless they can compete with your damage output. Deals around 22k critical damage.
Meteor Strike is a fire and forget skill with an incredibly wide balance range. It'll deal anywhere from 25~85k end-game, so don't rely on it to wipe out a group of tough enemies. It's best used on Round 3 of the NPC tournament or in any other situations where it's worth the 10 second charge time. Claimh Solas and the Doppelganger are great enemies to use this skill on. Make sure to communicate your use of the skill with your party to prevent it from being wasted.
Also note that you're not limited to magic skills. Windmill, Doppelganger, Counter, Defense, Charge, and Final Hit are also very useful skills for quickly recovering during combat.