Veigar suffers from low mobility and durability, making him reliant on his allies to protect him. His Dark Matter's and Event Horizon are both delayed, making him especially vulnerable to being initiated upon as he will do little to nothing before his death.
If you don't already use smart cast, consider it when playing Veigar. His kit has high damage but is heavily reliant on landing his combo of spells as fast as possible; choosing smart cast will make it easier to use all spells at once, especially when using additional skills such as Ignite.
Keep track of your mana pool, especially in the early game. If you simply use Baleful Strike only to farm, the enemy will soon start to harass you; juggling between using Baleful Strike with auto attacks on enemies while still farming minions is key to dominating a lane early game.
Be firm about the Crest of Insight. Having the extra CDR on Baleful Strike will let you hit every minion with it and have the mana to sustain farming and harassing.
Early ranks of Baleful Strike have a higher cooldown, so remember to also use your auto-attacks to get last hits.
Try to dual last-hit minions for double the AP gain with Baleful Strike when given the chance, as it will greatly speed up his rate of achieving dominance later in the game. With decent itemisation for AP you should be able to double-tap ranged minions from full health, or 1 ranged minion and 1 half-damaged melee minion.
An easy way to last hit with Baleful Strike is to let the tower hit melee minions twice then follow it with a Baleful Strike. Let the tower hit caster minions once along with one auto attack and a Baleful Strike.
If possible, try to finish off enemy champions with Baleful Strike. It'll give you 2 more AP, in addition to the passive AP gain after killing an enemy champion.
Event Horizon is one of the strongest stuns in the game - it will interrupt dashes, stuns for 2.5 seconds at max rank and is area of effect. With practice, it's easy to stun, cage, or zone at least 2-3 players.
To escape, Event Horizon can be used to block off a choke point, or in the jungle an entire pathway.
Consider further leveling of Event Horizon if the stun isn't holding enemies long enough for Dark Matter's to land. This is usually due to Tenacity or similar individual champion abilities. Since Dark Matter is one of the hardest hitting skills in your kit, it is another key to dominating your lane all so that you can farm using Baleful Strike with less harassment from a passive enemy.
Be wary that Event Horizon is no longer instantaneous and comes with a 0.5 second delay to cast, being unable to immediately stun as it used to with its edge. Unlike other stuns, it will interrupt dashes such as Distortion and Resonating Strike, allowing Veigar to nuke them off-guard.
Always be more cautious when Event Horizon is not available, as it is one of Veigar's most important abilities. It has a long cooldown, making Veigar an easy target when it's unavailable, especially against enemies with high mobility and damage (like Fizz).
You can use Dark Matter's impact animation to corner your foes; place the spell near the champion but angled towards the direction in which he is most likely to retreat.
Starting from level 4 of Dark Matter you can use it for killing half a whole minion wave, as it instantly kills minions by then.
Placing a ward at the enemy Crimson Raptor camp means you can use Dark Matter and Baleful Strike to clear it whenever it spawns for easy gold and XP that the enemy jungler is denied. Care should be taken as to missing opponents and the location of the jungler when attempting this, however.
Always check to make sure that there is no one blocking Veigar's target if you're planning to use his nuke combo. Baleful Strike can only hit up to two targets in a linear fashion, and will be wasted if there are more than one enemy in between, leaving his opponent alive for a time to escape or to counterattack.
An advanced tactic is to use Dark Matter before landing Event Horizon. While it is difficult to master, if you have aimed both spells correctly the enemy won’t be able to escape before the Dark Matter can land.
Another advanced tactic, you can sometimes use Event Horizon to bait an enemy with a skill / ability such as Cleanse, place the stun just near them but without actually stunning them, they may activate their Cleanse simply believing they are removing your stun and then still walk into your stun ring.
Veigar has good synergy with tanks that build armor such as Rammus and Malphite. Because Primordial Burst punishes champions who build AP, this will force the enemy team to play attack damage based champions or build ability power based champions with attack damage builds (including certain ability power scaling champions like Kennen, Lulu, Kayle, Nidalee, Akali, Fizz, and Teemo where the said champions are known for their build flexibility). This in turn will allow Rammus and Malphite to simply build armor and health items to mitigate the enemy team's attack damage and allow Veigar to burst down the enemy team with his magic damage.
A Void Staff is almost always a necessary item for Veigar as enemies will likely be building a lot of magic resist to survive your damage output, if you are having a good laning phase also consider buying this before a Needlessly Large Rod item, as you will have already stacked 100 ap from your Baleful Strike alone, propelling you into your late game dominating mode fast.
Luden's Echo or Lich Bane often gives Veigar stats he secretly likes, extra move speed, both give extra damage procs and Lich Bane also gives 10% cooldown.
Because Veigar can just build AP from his farm, you can often afford to substitute offensive items with purely defensive or high utility loaded into them, and you can still leave the first few laning trips with more AP than the majority of other mages.
It is often viable gear Veigar defensively, especially if you're carrying, the enemy will prioritize killing you and many team comps will lack strong initiation leaving you feeling like you have to initiate with your Event Horizon in order to get anything done, the following items are suggestions to help you get your burst out before you fall.
Veigar as a mage has low mobility, high cooldowns and low mana regen, utility items can help, especially in terms of mana regen items, one thing to always take into account is your passive Equilibrium will boost any mana regenerating passives you receive.
Chalice of Harmony doubles with your passive Equilibrium, ensuring that you almost always never go out of mana. It can later be upgraded into Athene's Unholy Grail for the much needed cooldown reduction along with being able to restore nearly a third of your maximum mana on kill or assist, which can also be more than doubled, effectively restoring him around half of his max mana.
Sometimes using Spell vamp items/runes can improve Veigar's's sustain vs poking opponents. It will however, hinder his damage output, note with the changes to Baleful Strike, it is now 1/3 as effective.
ZoningVeigar during the laning phase will deny him from farming ability power from last-hitting minions with his Baleful Strike as he is fairly squishy and weak at early game.
This is important because if Veigar is allowed to farm and get items and ability power, his combo will be lethal late-game, being able to instantly kill almost any champion. The only champions who can survive his combo are bruisers and tanks with a lot of health and magic resistance, and even then, it will take more than half of their health, leaving them low enough for any ally to pick them off.
Unlike other champions with stats that can increase infinitely, such as Nasus and Sion, Veigar is built with items that leave him very squishy himself. Due to this, it is imperative to avoid being stunned by Event Horizon; if you dodge it, burst Veigar down.
Although Dark Matter deals massive damage, it has a considerable delay before it lands. Use this to avoid the spell.
If the wall of Event Horizon misses you during placement, avoid walking into the wall as it will still stun you for the full duration.
Pay attention to Veigar's cooldowns. If Veigar uses Event Horizon or Primordial Burst (or both), this is where he is the most vulnerable. Take the opportunity to kill him as fast as possible.
A common mistake amongst mages is to build Sorcerer's Shoes when laning against Veigar, when they should build Mercury's Treads instead. While the extra damage will be missed due to not having magic penetration, the extra magic resist and tenacity are helpful due to Event Horizon. The sooner you get rid of the stun, the better chances you have to survive Veigar's combo.
In fact, it is recommended to build Mercury's Treads on any champion on your team if there is a Veigar on the enemy team, as it will decrease the chances of him being able to land his mortal spell combo.
As a purely combo based mage, buying a Banshee's Veil is an excellent way to counter him as it essentially negates one of his spells, making him unable to initially unleash a full combo upon you.
If Veigar is giving you a hard time in early game if you are AP, try rushing a Negatron Cloak and build it into an Abyssal Scepter as he will no longer be able to successfully harass you until he has his Void Staff. Champions like Galio with a naturally high magic resist have the advantage over Veigar.
Be careful while building a team consisting of attack damage builds, as Veigar can counter that by asking one of his teammates to play a champion that punishes attack damage heavy builds such as Malphite or Rammus.
The majority of Veigar's damage output is magic damage, hence items such as Banshee's Veil will mitigate his damage output by a large margin. Banshee's Veil also negates one of his spells, which is vital, since Veigar is a combo-based champion.
Kayle'sIntervention can leave allied champions completely immune to Veigar's combo, making Kayle somewhat of an indirect counter to him. But if Veigar decides to focus Kayle herself, if she is stunned by Event Horizon, she can't cast Intervention on herself, and will fall to his spells just like any other AP champion.