In dominion, it is important to survive a long time, mobilty is also neseccary but above all, you have to be able to hit hard so enemies will absolutely be afraid of you. If you're very tanky but unable to do damage the enemy will simply ignore you. If you're doing alot of damage but don't buy any defensive items you'll end up being dead focused because you're easy to kill. So it is important to find a balance between these facts.

For this guide I will talk about Galio. Galio is a bulky champion meant to be a support tank. However his passive Runic Skin makes him able to be more than just a simple support tank that needs some AP to get enough attention to be attacked.

With the new update that came up the mastery tree has been changed and new summoner spells have been added. With this new update mastery trees became more efficient, and a better method to build up Galio with the mastery tree.

I go for 1/17/12

We build Galio up so he has a great sustainability in the field, which means: Enough mana regeneration and ability to bare a lot of damage.

In the defensive tree I go HP as well as some extra armor and MR. MR stays important with the AP you want to gain, while Health Regen makes sure you can sustain longer. AoE spells will do less damage on you, to make sure you can hold your point without it being rained down with AoE spells.

All Summoner Spells got fused together in three seperate masteries, but unfortunately my main spells are in two diffrent masteries. You can choose if you really want the extra 35% movement speed on however, that is when you go for my summonerspell combination. Utility mainly contains my mana regeneration and possibly some extra duration on the speedbuff and storm shield you can gain in dominion.

I repeat here, magic resist. The Glyph and the Quint give a fair amount of MR And you know it, the Runic Skin converts half of the MR into AP. Making him both defensive and offensive.

The Greater Seal of Scaling Mana Regeneration is for the extra mana regen so galio can sustain longer in the battle field.

And the Greater Mark of Magic Penetration for more damage output.

Reccomended:
Gives great mobility over the field and can help you get away.
Combine this one with Idol of Durand. Or just to save yourself when you get too much CC to be able to escape properly.

Other Possibilities:
I suggest not to use this one though. You'll regenerate mana fast enough to be able to fight. And if you don't there are healthpacks littered everywhere containing mana and hp.
Could contain a bit of suprise on a enemy who just killed you and is trying to take over the capture point near your base. Although I won't see a reason for someone making a bulky build dying alot as well as the death counter isn't that high in dominion.
Only useful when you get massively CC'd. Furthermore I don't see this as your best option since you'll never know if they mass focus you. If they do you also have the option to buy a Quicksilver Sash
Combined with Idol of Durand could be a strong combination. But Galio can be played in two ways: Defensive and Taking over capture points due his mobility.
I won't expect anyone taking this spell. If you truly want someone to die who is on low hp you got all kinds of abilities to catch up with your prey.
With the buff they gave to this spell this is another posibility for Galio. Gives you extra sustainability when you're truly cornered
For if you like pushing your minion wave forward. This thing can be a pain for the enemy since it can sustain pretty long.
Nope, Galio does not need any offensive upgrades. Even with the attackspeed and AP this thing gives I wouldn't say this is the most important skill on Galio.
Could be, but I wouldn't say so. Although it's good for chasing enemies and debuff them giving yourself some more sustainability against AD champions with their lowered stats.

The passive that makes it able to build galio both offensive and defensive against mages.
This is your main offensive spell. That's the reason why you buff up this ability first. It has a nice big range, slows your target and does quite a decent amount of damage.
The second spell to raise to level 5, it raises MR as well as armor, and can heal yourself, so this is often a forgotten AP boost on Galio.
This spell is great, it gives good mobility as well as a secondary offensive ability for you to throw at enemies.
You can use this ability in three ways: To save your allies from dying, hold a capture point, or because you ended up in a team fight and you're supposed to initiate.

I'll max out first to scare off enemies and damaging them badly. Starting with one in righteos gust which I will max as last since I'll use this spell for moblility. gives more hp the higher the level is as well as Armor and Resistance I'll max this one up second for more sustainability.

I've been scrolling through the entire list of defensive items, both MR and Armor and what might be strong combinations. These items caught my attention the most:

Standard:
It's simple, it gives tenacity and magic resistance. Giving Galio AP because of .
To help you sustain the first minutes of the battle since Galio is a little bit fragile early game.
mana potions Two of these help you through the first minutes since Galio's mana hungry early game.

Magic Resistance:
Reccomended items:
Gives a nice amount of magic resistance, gives quite a lot of AP and even lowers the magic resistance of every enemy champion nearby. An ideal item for offense.
It increases your movement speed, gives 45 health regenen combined with 0,35% of your health, and a nice 74 magic resistance. An ideal item for sustaining and mobility.
Replacement for banshee veil the creators said. With this item you should taunt mages to attack you with spells just to punish them back with the active of the veil. Deals damage to all enemies around you.
Another offensive based item with a little bit of MR, also gives more mobility and a passive that strenghtens your auto-attack.
ageis of the legion This item is meant to have when you walk alot along with your teammates to give them some bulkiness too.

Optional items:
It does give good MR, and has the same kind of effect as take it when you feel like you get CC'ed a lot.
Why an attackspeed item? It gives more MR each time you hit an enemy stacking up to 4 times. You can also chase your enemy and hit him a few times with a swift auto-attack. But I do admit that's a bit blunt for someone you try to build up using abilities.
I despise this item as you get enough mana regen ingame. Really you don't need it with all the healthpacks littered around, and you're more running than you're going to spam all your abilities. Even with the magic resist I say it's not worth buying this item at all.
If there is a reason I would take this one, it's for the CDR, the MR is too low to be worth it and with the you'll already come pretty far with healing yourself.

Armor:
I've had a few laughs with this item of people thinking like "I will die anyway, let's just try to damage him as much as I can." and end up dying because they get hurt by the thornmail. 100 Armor on it and hurting auto-attacking champions.
Armor, health, and dealing damage to all nearby enemies. How much more can you irritate enemies for 'just being there'?
Take this item if you fight against an AD team. You won't get much chance to build up any MR but you really need some AP to do damage. This item gives armor and 100 AP. Enough to make up for the missing AP you would usually get from getting MR.
One of the best Armor items ingame, 99 armor, lowering Attackspeed, 25% cooldown, and some extra mana. Good for countering those attackspeed based champions.
Massive slow on every enemy around you and lowering their attack speed, sounds like massive troll to me all they can do now is run for their lifes. Impossible with Galio's abilities that are focused on chasing.

Other Good Items:
If you find yourself dying alot a second chance to beat them up might be pretty terrifying for them. Also gives you quite some decent armor, health and MR.

Early game
Go for the windmill. Or the bottom capture point. I prefer the the windmill so you can support your team directly with your . Making them arrive earlier and have a small advantage over the other team. While you are there you'll harass with at this point the damage you deal to your enemies is enough to scare them off for a few seconds. Whenether one of your teammates is in heavy danger make a escape route for them with and hit the chaser with to make escape available for your ally.

Mid/Late game
Prefably you go defending but with the for Galio it's easy to move around capturing points and eventually backdoor when the enemy's busy with a teamfight on your teammates. However don't concentrate too much on capturing when you got three points. Domion can quickly turn from your favour into a disastrous situation that seems impossible to recover from. Galio is quite a bulky champion good at stalling enemies from capturing a point so USE it to your favour. Simply harassing them with and righteos gust is fine. And for more durabilty you always got as well as to keep your capture point safe. Punish champions coming too close or trying to capture right before your eyes.

Galio is good at supporting as stated. Very good at helping allies escape as well as chasing low HP champions. Use the to flip the team fight and save allies that cannot possibly survive otherwise. Ping for help whenether there's a strong champion at your capture point trying to take it.

I conclude, with these builds Galio is hard to kill and still does quite alot of damage, enough to fend them off and enough to be still called a threat instead of being ignored because he's just impossible to kill and a waste of time to try attack him. If you still got any questions or got any ideas to improve this guide you can post them in the comments.

Conclusion: They should come with more bad guys...

Not really much happened yet.
However now be more careful when you're fighting while this is a mage assasin contains true damage on the way back. You cannot block this with any defensive items. Make sure to evade Ahri alot while she uses this attack as well as her can get you off your capture point for a while.