Kog is not defined so much by “early, mid, late” as many other champs as far as their role is concerned. Rather, Kog’s power and presence is dictated by the rank of Living Artillery.
Rank 0 - Feeble Mortar Mimicry
Before you have your ult, your laning phase should consist of using your spells at maximum range to farm the waves.
- Survival is the name of the game
- Don't excessively push.
- If you die, you weren’t playing carefully enough
- Poke to farm
Farm with Void Ooze: Void Ooze is the most useful one for this task, as it has longer range than any of your other spells and its AOE is able to take out minions decently. Use the tip of its ~1,300 range to farm many of the minions. Trade Cautiously: AP Kog'maw has some decent trading early on which can punish enemies if they overccommit with their aggression. Actively harassing the enemy doesn't usually pay off however as AP Kog can't really confirm kills early. Land Incidental Damage: You may not be trying to poke opponents down, but incidental damage is always nice. Try to position yourself to hit both the minion and the opponent at the same time. Beware the Enemy Jungler: Kog is an easy target for the jungler to jump on. Unless you have a strong idea of where they are, you should prioritize playing safely rather than playing greedily. You'll have time to be greedy later. Go Back Instead of Pushing: Your pushing power isn't worthwhile this early. Unless the enemies have seriously screwed up, it’s not worth the risk compared to simply getting a nice reset. Get a Control Ward Against Flanks: Get an early control ward and set it up to protect from a jungler tower-dive ambush.
Always Improve at Surviving: Every death is preventable. It means you were too far without wards, you were trying to trade, you didn’t dodge enough, or you got surprised by burst damage. Take every death as a learning experience of what to expect for the future.
Use Unsealed Spellbook to Stall Longer: The two best spells to swap to early on Unsealed Spellbook are Teleport and Heal. The first to quickly refill on health + mana at level 6, while the other can be placed neatly over Barrier if Teleporting back isn't quite needed yet.
Rank 1 - Obnoxious Spittle Tickler
The first rank of the ult is your first major power spike, immediately doubling your power. Upon receiving it, your Barrage Limit starts at 1.
- Prevent opponents from roaming
- Force squishy targets back with powerful ooze-ult combos
- If you die during laning, you weren’t playing carefully enough.
- Use your basic spells primarily for their utility
- Poke to deter
Avoid Ulting Twice In a Row: Shooting even 2 bullets in a row is an easy way to use up your whole mana bar very fast, so carefully consider every time you even want to shoot just twice. Use Ooze + Ult to Clear Minions: If you use Void Ooze on the caster minions, the execute bonus of the ultimate will proc on them, allowing an instant clear on the minions. Deter Enemies With Ooze + Ult: Unless your opponent is very squishy, you should largely be using poke as a form of deterrence rather than a form of killing. Still, a successful ooze-ult combo on an opponent can deal substantial damage so always keep an eye out for chances to land one. Don't Let the Wave Build Up: You have the range to be able to pretty reliably keep killing the wave over and over at a distance, and you should use this so that enemies have a much stronger potential cost for roaming, as you can then rapidly push if necessary to get a greedy plate sometimes. Ward the Enemy's Half of the Lane: Your opponent will likely have their ult at this point as well and will often begin roaming, as Kog lacks the pushing power to take advantage of their disappearance. Putting wards on their side of the lane will ensure that if they begin roaming, you can warn which direction they go so your team will have heavy advance notice to get away.
Be Careful When Following Roams: You may sometimes want to chase after roaming opponents, but be aware that they may easily be hiding around a corner or in a bush in ambush, waiting to take advantage of your still-weak power. Alert your team, and be extremely cautious of ambushes if you choose to follow them.
Unsealed Spellbook Provides Durability: Good swaps at this point start being Exhaust and Heal, which add even further bulkiness with Kog's ample health and Resolve runes.
Rank 2 - Artillery's Apprentice
You have hit your second major power spike, doubling your power once again. Now that you are 4x more powerful, you may begin poking very offensively at the opponents.
- Keep everything constantly warded
- Clear waves instantly and begin pushing and grouping
- Be wary of dash-combos
- Poke to kill
Keep Mindful the Barrage Limit: Don't go trigger happy with ultimates. While the Barrage Limit is about 2 now, be conscious of how much mana is being depleted. Running out at the wrong time can give the enemy leeway for a tower. Use Spittle First: Caustic Spittle, Ooze, Ult, Auto. A committing target can’t avoid the Q, which will amplify the damage from the rest of the combo. Chain Aggressively: Your teamfight presence is now massive even with few items. Rylais will be finished soon and you'll get to start chaining opponents down. Careful however; a wide variety of dash-combos can still reach you even at max range. Scout With the Ult: Living Artillery grants vision on the location it casts on, so use it to see if the roaming mid-laner is trying to ambush you or if the opponents really are at baron. Ult Your Feet: During duels against melee targets, keep ult’ing at the ground directly underneath yourself. This will guarantee the hit unless the target decides to disengage momentarily, buying valuable time to make distance. Aim for the Zhonyas: Whenever you see someone has gone into Zhonya form, keep your eyes extra peeled on them and try to land an easy ult shot rightttt as the Zhonyas duration ends. Once you get good with the timing of your ult, the Zhonyas form is just a free target. Unsealed Spellbook Provides Options: At this point, the summoners from spellbook will start rotating. Ghost is a good replacement for Flash when it's on cooldown while Smite can be used to help secure an objective, or just to add more CDR onto Spellbook. It's tricky balancing unique spells vs. more useful ones.
Rank 3 - Ruler of the Acid Reign
This is it. If you have made the game go on this long, another 2x multiplier in power. You are now 8x more powerful and boy does it feel damn good.
- Stay at max range unless an engage happens
- Keep a target locked on and shoot
- Destroy diving opponents
- Poke to win
Abuse Your Range: You are now safe from almost every single dash-combo in the game at max range. Unless you are caught off guard due to poor warding, you cannot be reached except by flash-dash combos. Remain at max range unless it’s time to clean up, and continue buying constant wards to maximize your safety. Caustic Spittle the Tanks: Use your Caustic Spittle to slow down and shred tanks trying to dive into the middle of your team. If combo’d with your spells right after, a few empowered autos is enough to deal insane damage. Your Dueling is Good: Your dueling potential is extremely strong if you have exhaust from Unsealed Spellbook up. If the fight is starting to die down, consider getting closer to the fight and pick off the remaining opponents with your Bio-arcane autos, which now do fairly hefty damage in their own right. Flash + Ult: Opponents will often try to break your chaining by flashing out of it. Flash toward them to immediately close the gap and continue chaining. Also use to get the last bit of distance to snipe a flee’ing opponent, but be wary that if they’re not CC’d, they can dodge the ult and waste your flash. Use the Nexus Regen for Last Stands: In dire situations where you have to hold off several opponents from the nexus turrets, you are able to stand at the edge of the base regeneration and unleash a literally endless stream of bullets. This allows you to become the absolute final line of defense when things are looking grim. Chain a Backline Target: You can safely pick targets every fight who you want to hunt down and chain them to death. Often, just a 3 or 4 artillery chain is enough to send an opposing magician to a quarter health or less for one final execution shot. Pick a target and keep them locked on.