Hope you like the following 2moons guide which selected from the other website by me, but it's not my work, 2moons-dil just give it a summary. Hope it can help you some.
Tarantula vs. Grewpain: For the most part this is a pretty easy comparison. Most people find Tarantula better than Grewpain, and we think so as well. At Lower Levels(2moons gold) the fact that Tarantula can not only Poison Monsters, making it easier to kill at lower Levels, but he can also survive a lot longer. Grewpain just generally sucks.
Aldebaran vs. Regulus: Regulus may hit harder, but Aldebaran's Stun is what makes him very important and useful. Though both Summons technically do slow down the monster or w/e in a sense, but when it comes to higher Level Bosses where you may still use these Summons (mainly refering to Crespo Boss, the damage between both Summons are both so Low it doesn't even matter, but what does matter is the HP(2moons dil) and Def.
Because that will determine which Summon out of the 2 will last longer, and Aldebaran can tank alot longer than a Regulus can on a Crespo C Boss. We know Aldebaran has been Nerfed with recent Patches to kind of suck now, BUT either way if I were a high level bringing some noobs along for Free Crespo C or w/e idk we would want them to have an Aldebaran over a Regulus.
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