Recharging and Consuming Guide

Before recharging , always check the timed events.
Most of the times you will get special diamonds rewards for recharging certain amounts of diamonds.
Most of the times these rewards will be :
1) + 300 diamonds with 60 diamonds ( 1 euro ) recharge ,
2) + 900 diamonds with 1200/1800 diamonds  ( 20/30 euro ) recharge ,
3)+ 3000 gems with 6000 diamonds ( 100 euro ) recharge
Also on the first day of a new event , there will be an extra recharging or consuming timed event rewarding special chests, skills , materials based on your rank placement.
Recharge during recharging events to get the maximum benefits out of your money.
Last but not least ,  each event will have unique timed events rewarding event specific items. This can be either , wheel tokkens , chests or diamonds along with other rewards.
When the event specific timed event rewards diamonds you can get an extra 300 diamonds with 60 diamonds ( 1 euro ) recharge . In other words you can spend 1 euro and get 660 diamonds which would normally cost 11 euro!

There are a few things to think of before recharging.
The first thing you want to do before recharging is to check the timed events for any specific reward you might want to claim. Sometimes you can obtain fiends / bispirits / wings or other items with 20,30, or 100 euro recharge.
The second thing  you need to do is to check the diamonds rewards on timed events. Sometimes you can claim more diamonds by recharging 5 times 20 euro in 5 consecutive days other than recharging 100 euro in 1 recharge.
For example :
Case 1 ) With 100 euro you get : 6000 diamonds from recharge , + 6000 diamonds from x2 multiplier , + 300 from 60 diamonds timed event recharge , + 900 from 1200 diamonds timed event recharge , + 3000 from 6000 diamonds timed event recharge. Thats a total of 16200 diamonds  for 100 euro.
Case 2 )With 5 * 20 euro( 20 per day for 5 consecutive days) you can get : 5 * 1200 diamonds from recharge , + 5 *1200 from x2 multiplier ( if you have it ) , + 5 * 300 from 60 diamonds timed event recharge , + 5 * 900 from 1200 diamonds timed event recharge. Thats a total of 18000 diamonds for 100 euro. 1800 more than the straight 100 euro recharge.
Case 3 ) With 5*20 euro ( 20 per day for 5 consecutive days, but with multiplier expired ) : you can get 5* 1200 diamonds from recharge , + 5*300 from 60 diamonds timed event recharge , + 5 * 900 from 1200 diamonds timed event recharge . Thats a total of 12000 diamonds for 100 euro.  
Case 4 ) With 5*20 euro (20 per day for 5 consecutive days , but with only 4 multipliers available ) : you get 5*1200 from recharge , + 4*1200 from x2 multiplier , + 5*300 from 60 diamonds timed event recharge, + 5*900 from 1200 timed event recharge. Thats a total of 16800 diamonds , 600 more than recharging 100 at once.

To sum it up ,
You always need to check how many diamonds you can get from timed events with your available money. Divide your money in days , check if you have enough x2 multipliers for all days. If you do , recharging little every day will be more rewarding than recharging all money at once. If you dont , you need to calculate how much you can get with your available multipliers and decide what will be more rewarding for you.

Efficiently Recharging is all about mathematics. As i explained above in the "how to recharge" section , most of the times you can obain more diamondsby recharging little money every day rather than recharging a lot in one day .However , the bonus diamonds you claim are only worth 1/5 or less than the total amount you spend.
Of course more diamonds are always nice , but what if i told you there is a legal way to claim  6-10 times more diamonds than what you pay !
Mathematics will explain :
Weekly pack : cost 5 euro - awards 300 diamonds straightaway , +250 diamonds per day for 7 days , total of 2050 diamonds per 7 days with 5 euro.(8200 per 28 days with 20 euro)
Monthly pack : cost 8 euro - awards 480 diamonds straightaway , + 120 diamonds per day for 30 days , total of 4080 diamonds per 30 days with 8 euro.
1 euro recharge per day - awards 60 diamonds per day straightaway , + 300 or +600 diamonds per day from timed events, at least 10800 diamonds per 30 days with 30 euro.
Total of 23.080 diamonds per month with 58 euro per month . Normal Price for 23.080 diamonds is 193 euro with x2 multiplier or 385 euro without x2 multiplier.

However theres a small disadvantage to this method.
From the 23.080 diamonds you will claim in 30 days only 3.480 will come us account diamonds , the others will be character diamonds. That means you will only have 3480 diamonds availablefor items that require account diamonds. Luckily those items are just a few and the only really worth spending on, are the materials to compose thunder valley keys.Everything else you will need can be bought with character diamonds.

It is most wise to save your diamonds and spent them during consume events for top rewards. Consume events will always appear during the first day of a new event.
If you plan to play with minimum money spend , you dont need to spend on every event but only on a few.
You will want to spend only on events to gain the top items of each category .
Those items are :
For wings : Wings of Void or Phoenix Wings Event
For outfit : Peerless Wargod Outfit event
For mounts : Ice Wyvern , Flame King Kong and Jade Claw events. ( You will want to obtain all three of them , Jade Claw is the most powerfull mount , the other two have unique passives which are active even when you dont use those mounts  )
For warpets : Valkyrie , Alvit , Goddes of Light , Sea Princess ( You will want to obtain one of them , + 60 more of their pieces to evolve them to last phase )
For Bispirit : Shadow Spiritus Event
For Fiend : Destruction Fiend Event
You can spend on other items if you want too , but those are providing the maximum power boosts and are considered the best. If you have the best from each category , getting another one will only give a minimal boost from 4-10k power , which is not worth the large amounts of diamonds required to obtain them.