Ok, for the first, when you make custom card, it shouldn't have more than 4 lines of text. That's a rule you should always keep in mind. Luckily, you can just remove "from your deck", because Recruit is always from deck. Then, I think it's nice design. It's definetly not OP, because you need to put Magma Rager in your deck, which is crap when you draw it. Also, it's easy to kill, so opponent will mostly trigger Deathrattle, and you cannot play this for busted turn 1, because of Elemental requirement. One thing I would change is to remove "from your deck" and Recruit should be capitalized, like all keywords on all cards are.
I also removed Lifesteal, it was one effect too many.
I'd argue that this is just a better Assassin's Blade. As bad as Assassin's Blade was, this is miles better because of Poisonous being on the card. It's four minion removals for 1 mana more and discourages weapon removal – which isn't very fun for your opponent, as they can't even play around the card. Then again, it makes Rummaging Kobold viable. I don't know what to say other than upping the mana cost, but if you just compare this Arcanite Reaper or even Gorehowl it seems much more powerful, of course only if you aren't going face. As a legendary weapon, I'd honestly put this at 8 mana; maybe 7 but that's still pushing it. You did well to do away with Lifesteal though because the healing for 3 part isn't important, and is only relevant with weapon buffs (which isn't relevant for this weapon).