Hello Summoners!
I really disliked the builds for Elise on the net and I decided to make my own guide to enlighten your minds. As you know, Elise is an extremely squishy assassin / mage. But people are WRONG about something. Yes, she is an assassin but ONLY WHEN YOU BUILD HER TANKY => BUT if you go too much tanky, she will be even more worthless though. In this build I will teach you how to make balance between both being tanky and a pew pew killer.

FAQ:
1-) Q: Why do we max our W first?
A: Elise has very limited farming abilities. To be honest her only farming / aoe skill is her W. In human form, you need to send your volatile spiderling smartly to hit multiple creeps at once. And In spider form, W is the key to kill someone: IT GIVES HUGE (%140!) ATTACK SPEED BUFF. (click W and auto-attack as more as possible, without dying ofc)
2-) Q: Why do we max our Q second?
A: This is the only single- target damaging spell we have. Maxing this at 13 will give you the advantage of dealing DPS independent from items. And this is what you need while you are building her tanky at mid-game.
3-) Q: Why don't we max our E first rather than our Q?
A: Because, even at the max level its cd is kinda long. Right usage of E is how to take kills at 1v1 or 1v2. And to survive ofc. Look at the Combat Chapter for more information.

When you decided to KILL someone:
1-) ALWAYS START TO FIGHT IN HUMAN FORM, TRY TO SNIPE YOUR HUMAN ABILITES. ESPECIALLY YOUR E. THEN DIVE IN SPIDER FORM. PRESS W. KEEP RIGHT CLICKING TO YOUR TARGET. NEVER QUIT SPIDER FORM WHEN ESCAPING BEFORE YOUR HUMAN FORM E IS READY.
2-) Look at the enemy team. If they are stacked, and your team is not in combat, STAY AWAY. YOU ARE NOT A TEAM CRUSHER LIKE BRAND. YOU ARE A SUSTAINED AND CROWD CONTROL POWERED AKALI. SINGLE TARGET DPS DEALER.
3-) If your team is in combat with the enemy team, choose the weakest target, dive to him / her. If you killed someone, firstly use your E to become untargettable, then choose the second weakest target to attack, or run away.

FAQ:
1-) Q: What are our core items?
A: Frozen Heart, Haunting Guise, Sorcerer's Shoes, Rabaddon Cap and Guinsoo's Rageblade
2-) Q: Why are we building Frozen Mallet?
A: When you are chasing or escaping, Auto-attacking is more viable to slow. Rylai's Scepter is worthless against immune-to-next-spell abilities. Just like Morgana's Black Shield, Sivir's Spell Shield, and Banshee's Veil's unique passive. And it gives a huge amount of health, which will make you tanky.
3-) Q: Guinsoo's Rageblade??!?! REALLY?
A: Yes, yes, yes! Your ulti gives bonus damage to your auto-attacks when you are in spider-form. And it scales with your AP. Guinsoo's "FANTASTIC" Rageblade gives you Attack Speed (To proc more your passive) and bonus temporary Ability Power (To enhance your passive). And it gives AD and AP to enhance your stats. It is just FANTASTIC.
4-) Q: What are the situational items?
A: Look at your enemy team. They will give you the answer.
-If they have heavy AD: Stack Armor and HP with items like Sunfire Cape, Randuin's Omen etc.
-If they have heavy AP: Stack Magic Resist with items like Abyssal Scepter, Force Of Nature, Banshee's Veil
-If they have tanks and bruisers / or they are balanced: It's up to you. If you want to kill tanks, you can build Deathfire Grasp or Mardred's Bloodrazors (They are both viable imo)

MUST HAVE: FLASH
TEEMO IS RUNNING AWAY WITH 5 HP!: IGNITE / OR:
I WANT TO KILL TEEMO UNTIL HE GETS THE ADVANTAGE OF RUNNING AWAY: SURGE

Thanks for reading, I hope it will be helpful to you. Actually I own with this build and i make people say "Elise is OP! ******** Riot ban it!"

I hope this guide will be popular. Because it will encourage me to make new ones if it will be successful.