hi guys, I am currently a silver 1 player who climbed the elo thanks to kassadin. In low elo I recommend playing and learning it because the games tend to last a long time. I played a lot of games where the game seemed lost because the allied bot lost the second tower at 10 minutes and the inhibitor at 13. But thanks to the power of kassadin's level 16 I managed to overturn the game 1vs9.
I climbed with a friend (who usually played amumu) and I had a winrate above 70%.
unfortunately kassadin no longer has the ROA and with the new items he is no longer strong in late as before. He also has much less hp than before and above all Presence of Mind has been nerfed. However, now you will hear the luden's powerspike, you will be a champ even before level 16 and you can abuse champ like Ekko or Fizz even more.

Pros:
you can't lose a lot of matchup.
one of the strongest late games in the game
good splitpushing
good mobility
AOE damage

cons:
you can't win vs ad assassin
good farm
very dependent on mana (you always need bluebuff)
dependent on level and item
ITEM

he main item is Luden's Tempest. It gives you the main stats you need.
If you prefer some hp (RIP ROA) buy Everfrost.
Vs tanks buy Liandry's Torment or Riftmaker, choose the one you feel best with, they are both strong.
Archangel's Staff for additional mana.
Lich Bane it gives you a lot of damage that has a good synergy with your spam kit.
Don't understimate Frozen Heart: 400 mana (+ Riftwalk), 20 ability haste and 80 armor.
Rabadon's Deathcap for damage:D.

ABILITY
Void Stoneis broken vs ap. Thanks to it, you will not be able to die and you will survive the combos of Ahri, Vel'Koz etc. without many problems
Null Sphere very good synergy with the passive. is very strong for the shield, you will win any trade vs ap with this.
Nether Blade gives you back a lot of mana, helps you last hit the minions under the tower.
Force Pulse gives waveclear, slowdown, and especially aoe damage.
consider the skill counter to use before it activates. Maybe the enemy jungler is nearby and you can find out through this ability.
Riftwalk too much aoe damage, too much mobility and watch out for the mana you use.
use the ability in fight to do damage but also to dodge enemy skill shots like yasuo's Steel Tempest.


Early Game

normally try to play safe before 6. Let them push
if they try to hit you with an ability, cast the Q to parry the damage. at the first back try to return with Tear of the Goddess.
From level 6 onwards you can engage with R + A + W + E + Q.
Try to always make short trades.

Mid Game
start roaming in bot (if it is in a balanced situation) as soon as you clear the wave. Don't stay so long out of the lane and get help from the jungler for a 4vs2 dive. YOU MUST TAKE THE KILLS.
if someone starts teamfights in mid that you don't want to participate in, you can splitpush. ward the bushes and the jungle.

Late Game

if your team is low, use your teammates as shields and kill your opponents. YOU ALWAYS TAKE THE BLUEBUFF AND BE CAREFUL OF THE MANA DURING THE FIGHT. you can very well flank. Always target the weakest targets (adc for example). Don't be afraid because you do a lot more damage than you think.

Conclusion

this is my first guide, sorry for the english. The guide is aimed at beginners, giving an idea of ​​what the champ is like.
I hope you have learned the basics from this guide:D