Hello everybody, after going to this forum each day and seeing many, many of the same questions being asked over and over and over again, I decided to put forth the knowledge that I have of this class so far. This guide is subject to change. Any factual knowledge that is contributed to it will be put forth and edited into it, after requesting such from a Mod/Vgm.
Twin Blade or Staff
A summoner has 2 combat choices that it can select. One being Twin Blades, the other being Staff.
Twin Blades
This combat choice is a fast-paced and close up melee fighting style for the summoner. You will rely on speed of moves such as Blade Spin, Devils Wing, etc. Also, since you will be fighting the monsters up close and personal, having HP pots will be more important. As well as having Skin of The Foreign Realm.
Staff
This combat choice is a more magic-based, kill-from-a-distance fighting style for the summoner. You will rely on continuously pumping out magic spells to knock back the enemy, and try to get hit as least as possible. It is very similar to a mage. Knocking back your opponent from afar is key. Contrary to a Twin Blade summoner you will need mana pots with you in a plentiful supply as you get spells that eat more mana.
Note: Neither Twin Blade nor Staff is better than one or the other. They both have pros and cons in their respective fields. It all depends on which style you find more fun and better suited for your playing style.
Beast or Libido
A summoner has 2 choices of essential summon trees it can choose from.
Beast
Level 15 – Grewpain (Has strength of ice)
Attack = 175 – 264, HP = 2835, Defense = 73
Level 36 – Regulus (Has strength of lightning)
Attack = 849 – 1062, HP = 12248, Defense = 252
Level 58 – Selaim (Has strength of fire)
Attack = 1124 – 1696, HP = 29963, Defense = 574
Level 83 – Bregon (Has strength of fire)
Attack = 1691 – 2717, HP = 43924, Defense = 896
Libido
Level 15 – Tarantula
Attack = 184 – 203, HP = 4158, Defense = 79
Level 36 – Aldebaran
Attack = 784 – 980, HP = 16897, Defense = 277
Level 58 – Tentator
Attack = 1005 – 1367, HP = 39098, Defense = 607
Level 83 – Anadema
Attack = 1754 – 2056, HP = 58565, Defense = 987
Note: To see more extensive information of these summons, you can visit this link: http://2moons.mmosite.com/guide/class/vicious_summoner.shtml
Credits go to chrisreams07.

no!!
Beast
Level 15 – Grewpain (Has strength of ice)
Attack = 175 – 264, HP = 2835, Defense = 73
Level 36 – Regulus (Has strength of lightning)
Attack = 849 – 1062, HP = 12248, Defense = 252
Level 58 – Selaim (Has strength of fire)
Attack = 1124 – 1696, HP = 29963, Defense = 574
Level 83 – Bregon (Has strength of fire)
Attack = 1691 – 2717, HP = 43924, Defense = 896
Libido
Level 15 – Tarantula
Attack = 184 – 203, HP = 4158, Defense = 79
Level 36 – Aldebaran
Attack = 784 – 980, HP = 16897, Defense = 277
Level 58 – Tentator
Attack = 1005 – 1367, HP = 39098, Defense = 607
Level 83 – Anadema
Attack = 1754 – 2056, HP = 58565, Defense = 987
noobb the beast have more str and less hp and libido less atack and more hp!
you forgot the last 2 pets…