Support Elise is what I coined as "ability support"
Ability supports are supports who are: AP based, can deal tons of poking and damage in the laning phase, Crowd Control and provide a good chunk of damage to the enemy ADC in team fights.
Compared to the usual supports, they are squishy and provides less defensive abilities or none at all.

She isn't widely accepted of her capabilities of a support yet, and the community won't take it lightly.
So take precaution because 90% of the time, people will think you are troll gaming.
This guide is newbie-friendly and is recommended for those who want to try her capabilities as a support with tips on how to play her without risking the victory of your team.
Season 3 Support Elise:

PROS:
*High Damage Output
*Maximum zoning and bursting in laning phase.
*Spiderlings in Spiderform provide a great shield to Blitzcrank-pull.
*Different skillset that you can utilize in bottom lane.
*Rappel escape tool
*3-second ward (not that good, but saves your *** a lot of times, it's a better option than to facecheck)
CONS:
*People will think you are trolling since support Elise is labeled inviable by majority of LoL players.
*Very Squishy and once the enemy CC's you, you're pretty much dead.
*No peel for your AD Carry
*Hard to perform the combo if you miss you Cocoon skillshot.

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You'll need magic and hybrid penetration marks for Elise since you'll be auto-attacking a lot and primarily deal damage with your skills.
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The armor seals are a must in bot-lane since you'll be facing a champion who deals physical damage and relies on getting Attack Damage to kill you and your team.
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AP supports were very popular during Season 3 and they continue to show up in the bottom lane even this Season 4 with their high-damaging and irritating pokes. These flat magic resist glyphs will ensure you take decreased damage from their skills.
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Magic Penetration Quintessences would allow your Neurotoxin/Venomous Bite to pass through their stale magic resistances early on in the game.

These are the best runes you can put on Support Elise , for they will maximize your potential in bottom lane.
But, I will put some substitutes for my runes. The substitutes aren't the best, but they will do.

You may be only trying out "Support Elise" so I included these substitutions for my primary guides.

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If you do not have hybrid penetration runes, you can switch them fully to magic penetration runes.
Don't have magic penetrations runes too? (what?)
Take armor marks then, it'll at least help you stack a few more armor.
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If you do not have any armor seals, you can substitute them with mana regeneration seals so you can spam more or you can trade them in for GPS seals if you like. After all, having more gold isn't such a bad thing.
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Flat ability power early on is quite okay, though you will be losing important magic resistance by losing the mr glyphs, magic penetration glyphs are okay too.
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Having health quintessences isn't bad actually, it's pretty good since it'll help you tank a few hits from attacks and skills. Having ap quints is another thing though, it's great I admit, but having base 15 ap won't make a difference early on, trust me. You'll need at least 20 ap to get add an extra 1% for your Q. But if you like, they're also good. :)


Like I said, they aren't the best. But they will do.

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Offense
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First off, we invest 5 points in the Offense mastery taking Sorcery for the cooldown reduction and Expose Weakness for the extra damage our adr could deal after poking the enemy with our skills.
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Defense
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Secondly, we invest 4 points in the Defense mastery taking Block for the reduced basic attack damage from both the enemy adr and support. Also Recovery for health regeneration in bot lane.
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Utility
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Lastly, we invest the remaining 21 points in the Utility mastery taking the vital Meditation for the mana regen, Culinary Master so we can upgrade health potions to Total Biscuit of Rejuvenation, then proceeding to take the gold per second perks as well as the cooldown reduction from Intelligence then finally Wanderer for the speed.

Source:askmrrobot.com
Q- Neurotoxin / Venomous Bite is your primary damage tool and deals high damage to enemies the higher hp they have and if in spider form, hurts more the lower hp they have. Max this first.
W- Volatile Spiderling / Skittering Frenzy is your harass(human),lifesteal or attack speed (spider) tool. Max this 2nd.
E- Cocoon / Rappel is your stun(human) / escape tool or your main skill to snare the enemy adr(spider). Leveling it up lowers the cooldown and increases the stun duration but nevertheless, max this last.
R- Spider Form / Human Form should be taken every time you have the chance as it makes your spider form stronger. Max this 3rd.

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Doran's Shield + 2x Total Biscuit of Rejuvenations are the standard starting items of ability power supports since they need to sustain themselves against the onslaught of pokes and harass by the enemy bot.

Do not forget, you are still a support, and whether the game is going good or not, you will need to rely on a GPS item. Spellthief's Edge will give you a decent extra amount of damage added to your harass and pokes early on.

Haunting guise is a cheap and worth-it-item to get early on in the game, it gives you HP, AP and Magic penetration which would be enough for you to getting started in trading pokes in bot lane.

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Situation: Your ADR or your teammates are constantly being instantaneously bursted down or killed and your Face of the mountain is not enough.

Mikael's Blessing provides magic resist and mana regen which both benefit Elise, the active basically heals 150+ 10% maximum hp of your adr's life and cleanses the debuffs off of them. Though this item does not provide any sort of extra damage for your skills but one of your main priorities is to keep the ADR alive, and this item solves that

Pretty self explanatory. Provides the team a passive health regen and 20 magic resist everytime you're near them. The active gives every ally around you a nice shield, probably to survive the first incoming AOE skills from the enemy AP, do not hesitate to activate the item when the teamfight starts.

Gives you lots of armor and a pretty amount of mana. But the best thing about this item is that it slows the nearby enemies' attack speed by 20% which would make the enemy ADR's job of killing your team, hard.

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5/5 Draven is very good at pinning and trading very early on in the game thanks to his very deadly Spinning Axe, he is usually paired with kill-lane supports. Hence, Support Elise matches with him very well.

4.5/5 Graves is tanky, has an escape skill and an ultimate ( Collateral Damage) that can immediately rip the enemy's health down to chunks, Elise can be paired very well with him.

4.5/5 Jinx thrives when she kills, that she can secure another kill after getting one. Her kit is also built on disabling enemies from escaping (like Flame Chompers!, a very nice combination with Elise's kit.

3.5/5 Twitch can damage very well thanks to his expunge but he has to stack his Deadly Venom before popping it up, if Elise manages to keep a grab on the enemy bot while he stacks up, it can be deadly and lethal for the enemy team.

3.5/5 Lucian zones very well with his skills, especially Piercing Light. His passive and ability to trade so well early on in the game makes him a good partner for Elise.

4/5 Varus is dangerous when he manages to get his blight stacks up and if Elise manages to ensnare an enemy champion he can quickly back it up with Hail of Arrows to slow them down and reduce their healing regeneration.

MAIN SUMMONER SPELLS

Flash- Out of all summoner spells I will list down here, Flash is a must for this champion. It's a beautiful and handy escape tool when your Rappel is on cooldown or has no targets and for chasing down low-hp enemy champions.

Ignite- Elise is a kill-lane support so therefore we must add this summoner spell in our arsenal of skills. Ignite applies true damage per second. the damage applied depending on your level. The skill also decreases the targeted champion's regeneration of health from lifesteal, heal, or health regen.

VIABLE SUMMONER SPELLS/SUBSTITUTE FOR IGNITE

Exhaust: The spell slows down the targeted champion, reduces the damage they deal and their attack speed as well for 2.5 seconds. Supports usually take this spell to disable the enemy ADR. Since Elise doesn't have any other cc than her Cocoon skill, this summoner spell is pretty good for her.

Heal- For those who feel like their adr should need a "pretty-okay" chunk of health during a trade or team fight.

LANING PHASE/EARLY GAME

Be aggressive by poking and zoning out the enemy duos at bottom lane (DO NOT CS unless you want to consume your Relic Shield's stack.). If you manage to successfully hit your E on either one of them, proceed to Q-W-R-E-W-Q. This combo can deal tons of damage to squishy carries or supports. This will also zone them out to towerhugging.
If you're ADR is good as you are, you will have a hug chance of dominating bottom lane.
Remember, be aggressive but not to the point where you are endangering your ADR and yourself.

(My)Elise Combo:

-> -> -> -> -> ->
(This is the most practical way of doing a combo using Elise, this is how you will harass the enemy during the laning phase. A combo of this would at least leave them half health or below.)

P.S.- When taking early Dragon, you can tank the Dragon by hitting it upfront using your spiderform, and let your spiderlings tank all the damage.

(Each Spiderling can tank 2 attacks from the Dragon.)

Always use spider form when warding alone or going back to your lane, you move much faster than in human form.

MID GAME-LATE GAME

Around this time, people will be moving around the map. SO it is very crucial to ward near the Dragon's lair and around Baron. (Baron is usually taken around 25-40 minutes in the game, but you can never be too sure.) Be careful when moving around the map, be map aware.

TEAMFIGHTS

When the 2 enemy teams are getting ready for a clash, never be afraid to spam your W Volatile Spiderling / Skittering Frenzy and if you can, Constant Q's Neurotoxin / Venomous Bite can deal a lot of damage.
Once the clash has been initiated, Cocoon/E Cocoon / Rappel the first one who gets near your ADR while constantly throwing out Q/W and once you have the enemy adr on your sights proceed to use the combo I listed above. This will force the enemy ADR to retreat or enemies will try to help the ADR leaving their backs open for your team. BE WARY OF THE ENEMY SUPPORT. If they are good, They CAN and WILL try to stop you. Find a good opening to Rappel on the enemy ADR. (If the enemy ADR isn't sighted or is too far away, don't be picky. Jump on the AP Carry or anybody you can jump on.) Play Video
Here, you could see in my ( mediocre) video how you could quickly turn the tide of battle if you know what you are doing, (or if the Leona didn't try to run away) never hesitate to secure the kill if you know your ADR cannot finish the job. As I try to towerdive the Miss Fortune and escape, you could see my spiderlings tanking the turret for me (Mama Love <3).
Oh by the way, in the end, we did kill the Orianna, but it was more of enemy stupidity than pro skills.

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Wards are the key to win the game and if you haven't bought your Sightstone yet. Don't leave home without them, even a single ward can at least provide you safety in an area/ route.

It is also Garen-approved.
"So don't think twice. Just buy buy buy~" -Garen
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But then again, buying wards and not knowing where to put them can be a serious problem.
Here are images showing the right way to plant wards.
Invisible text!These two areas should be warded at most, if not at all times. These are the usual routes the enemy jungler passes through to gank your lane, the other route is through the side bushes underneath the bottom lane.
If you are in the purple team ward the bottom left bush.
If you are in the blue team ward the bottom right bush.
Now unless there are long-distance response ganks like from Twisted Fate, Nocturne, Pantheon, etc. etc. or anyone with teleports. You should be safe (not guaranteed, lol).
Invisible text!This is where we usually put our Vision Ward so we can keep an eye out on dragon as well as the river where we will be warned off real early if there is a jungler or enemy mid coming to gank, it also helps clear pesky wards planted in the middle of the river.

Q/A
1. Q-What are the qualifications to use Support Elise in a game?
A- Your Mid laner is either an AD champ bruiser (Talon,Kha'zix,Pantheon,etc.etc.) or your AP is AOE-based. (Morgana,Heimerdinger, Viktor etc.etc.)
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2. Q- What makes Elise support special?
A- She can burst so early on thanks to her Neurotoxin's damage being calculated through how much health her enemy has. Also, she has lots of skills to back up her in trades down in bottom lane. She can initiate the gank so the jungler can come respond.
Later on, she is terrifying as she can burst down the enemy carries really quick and through that, she can protect her as well.
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3.Q- Is it worth playing her?
A- If you are trying out new builds, and looking for a way to innovate champions, then you are welcome to build her as a support, it is a very fun and rewarding experience, it takes time to master her as you just don't go in and deal as much damage, you also have to keep an eye out on your adr.

Elise Support is a very fun character to use, feel free to improvise the way you build your support Elise to your own accord, just do not forget that being the support, you have an obligation to protect the ADR and the team, buy items that could affect and help the team and yourself.
Enjoy yourself in the league, summoner. :)
-JeffStrife
(By the way, if you are in the Philippines Server add me, Avarosa)

I have changed my name from CB.JeffStrife to AvarosaInvisible text!
I'm a Diamond 2 player, if you play as an ADR,
Add me, then we'll play. :)

3/26/14 - Finished editing guide for Season 4. Shout out to Rezuki Kun, PKMN.Zapdos, PB.Oreygetong, Tenma and Happy Pig for helping me finish this guide. :)
3/24/14 - Revamping whole guide for Season 4.
5/24/13 - Added Abyssal Mask in Itemization and organized item cheat sheet.
5/31/13 - Replaced Greater Glyph of Ability Power with Greater Glyph of Scaling Ability Power
7/7/13 - Added Item Sets 1 and 2 in item cheat sheet.
7/31/13- Elise nerfed (Spiderling health lowered a lot)