Have you ever played AP Galio and noticed that, even destroying your lane, you don't deal any damage in the mid to late game? I find that frustrating, even when I'm one full item ahead of my enemy laner, he can sometimes be more relevant than me, and then I had a conversation with a friend, and although I always knew that one very strong aspect about Galio is his map presence, I never realised his damage is important in this regard, since it makes him have one of the fastest waveclears in the game. But again I though, can't I build Galio in such a way that I have great map presence but also peel for my team like Shen does, but more focused on tanking magic damage rather than physical damage? That's my idea for this build, and that's what I'm currently testing. The build is made for you to have a strong secondary engage and peel for your team, which requires map presence, damage, resistance, and extra shields. I don't think tank Galio is bad, but I think he loses some potential when building armor and not even a little AP, so this build is very MR heavy, meaning it's a situational build.

For this build, I'm taking advantage of the fact that, the same way malphite has an amazing synergy with armor, Galio has an amazing synergy with Magic Resitance. His passive's damage scales 60% with MR, he has a damage reduction while and immediately after casting his W that also scales with MR. Also, just like Malphite with his granite shield (a physical damage shield), Galio passively has (built in his W) a magic shield that pops with a certain cooldown, this shield scales with Galio's maximum health, and when he ults he gives everyone in the area of the ult the same shield he has (which is 15% of his health, a lot to an adc for instance).

Unfortunately, I don't think one could consistently build Fimbulwinter on him, it would be amazing and give him a ton of health, but sometimes the situation calls urgently for a Thornmail, or an Anathema's (which at least gives a lot of health too). Anyways, the build, as you can see, is aimed at trying to find a balance between these qualities Galio has.

As stated previously, this build is very situational. Galio excels at dealing with champions that deal mostly magic damage, so the first thing you need to look at before using this build is the enemy comp: Are they very AP heavy? Do they have more than one hyperscaling AD champion? If the answer to the second question is yes, you should probably avoid using this build. But, if all the AD threats are early game champions, and mid to late game the enemy team is depends a lot on magic damage, than this build should work.

There is one more thing: Your team needs to synergyze with you, you are lacking damage after all. First things first, considering the support is not building damage, your 3 other members of the team need to be strong carries, carries that you and the support will protect with your life. Not only that, you need a good engage aside from yourself so you can reengage with your ult, extracting more of the champion. Preferably this extra engage is not the support (I'll explain why briefly), which actually narrows down a lot, the perfect pick I can think of being Diana in the Jungle (she is a very strong carry that can engage very well and survive there), Jarvan is a good pick but he scales terribly, so I don't think it's the best option. Many toplaners can to this too, Camille being one classic Galio pair, she can TP flank the enemy team and then you can ult on top of her. Last but not least, your team needs a strong teamfight, which is not Camille's best quality, but it is Diana's, so I strongly recommend Diana to be a priority pick to pair with this build.

About engage supports, I think the ideal comp for this build is: You, A strong engage/high teamfight damage jungler, an enchanter support, a hypercarry ADC and a toplaner that fits the rest of the bunch. The reason for that is because if you have a hypercarry ADC, he will have both an enchanter to protect him in case someone gets too close (and also helping the frontline if possible) and a tank support that has some peel but mainly attracts everyone to hit him (with W) and has tons of CC to avoid someone gets close to that ADC. If you combine that with a lot of damage in the jungle and/or toplane, I believe we have the formula for a strong explosive team that is also able to protect their carries very well, a team with lots of engage, damage and protection. But again, I could be wrong, so ...

If you ever played Galio mid, I can simply say: Just play the same as always. Galio is surprisingly a lane bully, you have a decent poke to zone opponents and wear them down slowly, and you have a very easy engage and setup with a very strong combo that will deal a lot of damage, so use that pressure to your advantage. It is kind of hard to freeze your lane with Galio, since you have no control over his passive, but if yout opponent is not controlling his wave, it's easy to maintain your wave control simply smashing with your passive in the minions that have the less proximity to other minions. If you want to push, a simple Q+auto with your passive up should insta kill caster minions and deal some damage to a few melee minions, and from that point on just spam autos and skills on these minions, remember that Galio is kind of bad at pushing canon waves.

When you have your ultimate, you will play kind of like a Shen, always aware of what's happening around the whole map, especially your jungle. If he is invaded and you don't instantly ult, there is no reason to play Galio. If he is entering the enemy jungle, already position yourself as close to ult range as possible so you can ult him in case he facechecks the enemy jungler. Objective up? You can stay in lane longer than most midlaners to push, and then when a fight breaks out, you ult whoever you think needs more, your mentality should always be playing around your team and around objectives.