Alright so this guide will be more toward the newer players, although I will leave suggestions for the function so older players have something useful in here also.

Now about 8 Gates, it's a function that gives solid stats/power at the cost of coins only which is great. (there is an option to spend coupon/ingots on it put I do not recommend to do that ever)

Firstly let's look at how the function works:

a) First thing you see will be "Ask for help", that way you will receive a random 8 gate chakra. The further you go the better chakra you obtain and the coins cost increases (all are based on random chances and luck, there is no set threshold and for example "You need to use 10 mil coins for a red chakra" type of sentences are just rumors and are not true)

b) The further you go the more "Practice Points" you'll receive also from each one, the practice points are exchanged for whichever chakra you want and I would highly recommend to aim simply for the purple Quick chakra for starters.

In future when the exchange shop is updated you might consider getting a gold initiative or an important red one.

c) "Call Guy" option uses 100 coupons to "ask for help" the last ninja which is Guy, it provides the highest points and best chakra always however I highly do not recommend doing this, as you can reach him easily thru coins also.

d) Auto Practice, One-Click Sell,Accept,Synthesize is what you should always use when using bigger amounts of coins.

"Auto Practice" simply runs thru the "Ask for help" by itself until you have full slots.

"One-Click Sell" will sell all the empty chakra you received.

"One-Click Accept" I recommend never using unless you have only 1 chakra in the slot, otherwise your inventory will be full of useless chakras.

"One-Click Synthesize" will simply feed the highest color chakra in your current slow, which means all the other ones will be used as exp for it.

Chakra colors in the order of worst to best:

Green = common

Blue = uncommon

Purple = rare

Golden = super rare

Red = ultra rare

Note: The worse colors can not use better colors as exp (example: You CAN NOT use gold chakra as exp for purple one, the purple one will get destroyed)

the reason I am saying this is because I witnessed a lot of players lose their purple initiative chakra thru this mistake, be careful.

Now let's go to a more important part, where you actually equip and use your 8 Gates.

We have 5 main stats and 9 secondary stats and those are:

Main stats

a) Lightning (Ninjutsu)

b) Fire (Attack)

c) Water (Life)

d) Earth (Defense)

e) Wind (Resistance)

Secondary Stats

a) Quick (Initiative)

b) Inferno (Injury)

c) Scorch (Tai Pen)

d) Corrosion (Nin Pen)

e) Explosion (Critical)

f) Gale (Combo)

g) Ice (Control)

h) Sand (Damage Reduction)

i) Wood (Life Recovery)

With that said, you can only equip max 8 of them and the last slot is unlocked at level 100.

Which means you can only use a bit more than half of them, therefore you have to choose wisely.

About their levels, max is level 11 and optimal (to the point it's so expensive) level are 10 for gold and 9 for red (purple is easy to max level)

So it all really depends on your play-style and your current lineup, however I can tell you which ones you can exclude from your right away except in rare cases:

Life Recovery (It provides a passive heal for a ninjas after each round but it's a small one, pretty much never use this one)

Combo (you could use it on such ninjas as Jonin Minato who have good benefit from combo, however generally not much recommended)

Control (good stat in some cases, if you are using a blitzy lineup without protection then this might help with bringing higher chance of control fail on you, otherwise can be really useful on control heavy ninjas also to improve their chance of control (example: Masked Man) )

Now I'll write short descriptions/recommendations for other "good" stats:

Attack (Pretty straightforward one, you use it on damage dealer who prefers Taijutsu, but since most ninjas have tai/nin in their skill you'd prefer to use both atk/nin, however mostly useless stat for support type ninjas)

Ninjutsu (See above ^)

Life (A very useful one for pretty much any ninja, it's not a bad idea to use it on all, especially if you are running teams which are more based on survival such as Water Main healer teams)

Defense (A simple defensive stat, good vs taijutsu based attacks, mostly effective when using in front-row ninjas who are taking standard attacks from enemy)

Resistance (good vs ninjutsu based attacks, I mostly recommend using this stat on ninjas who give shields because all the shields in game are dependent on the ninja resistance)

Initiative (affecting the speed of your ninja, this one is a MUST to use at least on position 1 ninja, using on all other is optional however it's very useful if you want to win barriers and other ninjas going faster also)

Critical (useful for all as it will increase chances of critical and at same time decrease chances of receiving a critical hit, it's a must for main damage dealer(pos1) however optional for supports)

Injury (increases damage of critical hit and decreases damage taken from critical hit, also a must for main damage dealers however optional for supports)

Tai Pen (increases damage caused by Taijutsu attacks, highly recommend using this on damage dealer ninjas such as pos1, however it's useless for supports)

Nin Pen (see above ^)

Damage Reduction (decreases damage taken, highly recommended for support and front row ninjas without protection)

I will make some suggestions for you guys,however it always depends on a specific ninja:

Full damage (pos1) : Lightning, Fire, Quick, Inferno , Scorch , Corrosion. Explosion, Water(Earth,Wind,Sand)

Back row support: Water, Earth, Wind, Quick, Sand, Lightning(Fire), Inferno, Explosive

That would be all, if you have any questions or think I forgot to include something feel free to leave a comment !