Evelynn is an effective roamer. Use Shadow WalkShadow Walk to scout out and surprise enemy champions that overextend and possibly get a kill. This is most effective early game. By roaming, this allows your solo laner to farm minions while keeping the enemy solo back and losing them gold and experience.
Your Shadow WalkShadow Walk can be easily neutralized by Vision Wards early game. Don't be too hasty in attacking early. Take your time, scope out the battle before joining and use your element of surprise to your advantage.
With a maxed out Ravage attack speed boost, you need a 94.66% boost to reach the cap.
Evelynn is a great scout as she can walk past regular Sight Wards without being seen. Be wary of Vision Wards, as their true sight can detect stealth units.
Since Agony's EmbraceAgony's Embrace instantly deals % damage at a fairly large range. Evelynn can easily steal Baron or Dragon (damage is capped at 1000 vs them). With the shield and slow helping you escape any counter attack. Consider placing a ward so you can see the creature and arrive in time.
An early Sapphire Crystal or derivative item (Sheen is an excellent choice) will drastically improve the effectiveness of Shadow WalkShadow Walk's passive mana regen as its restoration is based on her maximum mana. 200 more mana adds an additional 2 mana regen per second, or 10 mana per 5 seconds, greater than even a Meki Pendant.
It also helps quickly stack Guinsoo's Rageblade making it very cost effective for a DPS build, but not a burst build since you won't have the stacks when you need to burst someone.
With both AD. AP, and a AS buff, Evelynn can effectivly mix and match any offensive item. See what defenses the enemy is building so you can adapt within your build. For instance, if they build Thornmail when you're playing Hybrid, build Wit's End instead of Trinity Force. If they all build Banshee's Veil then avoid building AP. If they build health, then Madred's Bloodrazor, or Deathfire Grasp with AP + CDR for your ult can help, but items with sustain such as Hextech Gunblade can let you fight tanks indefinitely, and can also be a good choice. Some good items are:
Note that Evelynn is inherently squishy, so any melee oriented builds must have some items devoted to tankiness, such as Guardian Angel or Randuin's Omen.
Since Ravage gives you 120% attack speed bonus, you can reach the 2.500 attack speed cap very easily (94.72% more at level 18). So it may not be wise to spend too much gold on attack speed items.
Speed items, such as Phantom Dancer andBoots of Mobility allow you to gank a lot faster and gain extra kills, keep enemies more uncertain where you are, and help you escape if you're seen out of position. Keep in mind that Slows are more powerful than Hastes (Movespeed buffs), and that movespeed items do not give much tankiness, so if you are caught or like going into melee range, a tankier item would be better thanks to the movespeed bonus from Dark FrenzyDark Frenzy.
Think twice before buying enemy affecting aura items such as Frozen Heart as the enemy can notice these affects from a distance, alerting them to your presence and possibly ruining your surprise. Ally affecting aura items can also be noticed, but with more difficulty. This is not an issue with Abyssal Scepter due to this item having only 600 range, while Evelynn's stealth range is 700.
Always look out for Evelynn in your lane. Because of her stealth, she can easily sneak behind unsuspecting players who are overextended. Be aware that her movement speed boost can make her very surprising.
You can protect your lane by purchasing Vision Wards and placing them in the river. Be careful if using Sight Wards as if she comes into your brush already stealthed, you will not be able to see her until she unstealths, and that may be too late.
Remember that when you play against an Evelynn, you do not want to push down her tower to early if she is solo top. Pushing down her tower before 20:00 can give her free farm, and even though you may have gotten a 150 gold bounty for taking down a tower for everyone on your team, her roaming abilities and free farm after you take her turret down are deadly, a good way to counter this is to let her minions push; and make her come out from behind her turret, leaving her open for a gank and great harassment, as Evelynn is extremely squishy early game.
Evelynn can be built with either Ability Power, Attack Damage or even a mix of both. Pay attention to the way she builds to better decide what defensive items you should buy. However, she still deals a lot of magic damage even with an Attack Damage build, so Magic Resistance is rarely a bad option against her.
If Evelynn is building AD, she has a very weak early and mediocre mid, but trades for extremely high damage late game. If you are a squishy champ, stay behind tanks and try to focus her down.