SKIP IF YOU DONT CARE WHO I AM AND WANT TO GO RIGHT INTO IT:
Hello guys!, My name is Taco and today I'll show you an amazing champ:
Rek'Sai, now if this is your first time going as her, follow this guide closely and you'll get the hang of her as easy as 123.

As of right now, she has received not a single nerf, so no need to panic about it.
Make sure you follow this closely, i tried to make this as small as possible so you dont have to read a whole lot.
Without further ado, lets start this!:

Now in runes, you have to go really standard to make sure you take the hang of her, you can modify them later.

Greater Quintessence of Attack Damage
We get Greater Quintessence of Attack Damage so that we can have an easier time farming minions (or CS) early in the game, and so that we can deal more damage to enemy champions. These stay useful through to mid game, until we grab some more damage items.

Greater Mark of Armor Penetration
As a general rule, we get Greater Seal of Armor Penetration so that we can deal more damage to the enemy from mid to late game, when people actually have armor. Now, if you wanted to have more early game potential, I would recommend going with either Greater Mark of Attack Damage for easier farming, or Greater Mark of Critical Chance if you plan on making trades.
Greater Seal of Armor
Armor seals have been the standard since I started playing this game, and while that recently changed, making it more of a choice between Greater Seal of Scaling Health and Greater Seal of Armor, I still find myself choosing the latter

Greater Glyph of Scaling Magic Resist
Finally we grab Greater Glyph of Scaling Magic Resist. These will provide a lot of magic resist late game and while they aren't as good early.

The masteries are so simple.
Just a 21/9/0 will do pretty good.

Everything we grab on here is just so our damage gets higher as the game on progresses, i think you might have the idea of how 21 offensive masteries work anyway.

All of the masteries in the defensive tree are geared towards making the early laning phase easier, while still scaling nicely into late game with all the resistances and damage reduction.

Items on her as on any other champion really depend on your way of playing her and the both teams, enemy and yours.

This is fairly simple, since it just depends on the enemy, the guide up top will be enough for you, but if you still want to go over this here we go:

Damaging as a jungler, specially a tankish one is a pretty important deal, since in teamfights the team will need us all a lot, thats why we get the tanky items on our list, and some damage for us to be someone that can get enemies as easy as do re mi.



Now, just by knowing the cc and abilities on your team and on the enemy team you can have a decent idea on what to build, i wont get too much into this topic.

It really depends on what is missing on your team, if your team has like no CC at all, just get your w first, it will do a lot of damage and you will work in team fights, if you feel like going E to deal much more damage, just level up like i indicated.

Pros:
She has amazing CC over all.
HUGE mobility, its amazing.
Your ultimate lets you Ult everywhere on the map (As long as you have portals of course)
Huge Damage if you focus on stacks.
Amazing Jungling, you can solo birds at level 1 and stay with enough health to do another camp.
Beautiful clear.
Nice assists in every teamfight.
NOT dependant on buffs.
Almost no skillshots.
Your Q in burrowed form has an amazing reach.

CONS:
If you struggle a lot early you may get behind and have a hard time.
Your Q is a skillshot and is based on Ap, so wont really do much.
Portals can be easily destroyed.

Jungling on her is easy, you just get near to monsters in burrowed form, q and then just unburrow and q again, then e once you have 100 fury.
Pretty basic.

You might want to counter jungle a little bit because of your early damage and high mobility, this is of course up to you and it depends on your way of playing her, but i can sure tell you it is going to work if you practice it.

Now spending a lot of time in the jungle is not the greatest idea, since you can also get stacks from assists so easily, your cleartime in the late game is stupid strong, so just take that in mind.

Tunneling over the jungle helps you get to team fights easier, and tunneling is really easy, just spam that e over your base to get to the jungle, then get tunnels to red, blue, dragon and baron, try to place enough so you dont have to move much. Having a 10 minute cooldown lets you use them for quite a while of time.

Ganking:
Gank with portals and hit them with your W so you get them flying up in the air, then q and go in burrow mode again to q with range just in case he tries to escape.

Tunneling gives a huge potential in the game.
Use the tunnels wisely.

In case you have no initiator, be the initiator! Get your W going on, and initiate with portals, get pretty tanky so you dont get killed instantly, make sure you tell your team you are going in since it may be hard to guess.

In case you have an initator just go in, do damage and stay there trying to defend your team, in case for a weird reason you are getting focused tunnel away and go back.

Teamfighting with her can either be beautifully executed or horribly bad played, you want to just stay in the center to deal as much damage as possible and going back every now and then, make sure you protect your team mates and make sure you use your E on the target once you have 100 fury to deal much more damage.