Lane and roam pressure with [R].
Creative tools and rule bending
Swap Summoner Spells while out of combat. Swapping to unique Summoner Spells will increase the rate at which you can make future swaps.
Gain a free stopwatch. Stopwatch has a one time use Stasis active.
Start the game with 6 Minion Dematerializers. Killing minions with the item gives permanent bonus damage vs. that minion type.
+5% Max CDR
+5% Summoner Spell CDR
+5% Item CDR
+22 Ability Power or +13 Attack Damage, Adaptive
Gain cooldown reduction and max cooldown reduction on your ultimate. This is increased further each time you use your ultimate, up to a maximum.
Gain increasing amounts of AD or AP, Adaptive over the course of the game.
Unsealed Spellbook on Galio gives you strong early game kill pressure by taking ignite. If you jungler comes in or a gank and you can layer your CC the ignite damage should get you an early lead.
If you're not able to get an opportunity to go for the kill, swap to TP for more map pressure.
A well-timed stopwatch can be the difference between life or death, and possibly even a kill. The sale of the broken watch also acts as an assists worth of gold income.
Minion Dematerializer helps in empowering your early-game wave clear so that you're able to keep up map pressure with side lane roams with your [R].
Cosmic Insight's all-around stat effectiveness is a great option for any champion. Combined with Unsealed Spellbook, your summoner Cooldown will be even lower.
Galio's mid-lane strength largely comes from his ability to roam and assist the jungler with your long-range [R]. Having [R] up more often massively empower's your team's strength.
Gathering Storm is a great late-game damage insurance rune. Galio tends to build a bit defensively and the extra bit of AP from Gathering Storm in long games can make you a strong frontline threat.
Patch 8.10 saw a buff to Phase Rush and jungle duels for scuttle making Xin a powerhouse.