Force bubble is potentially useful, since Mercs are ranged, though it does tend to aggro alot of enemies. Good for farming and a little fun, at least.
Scorpion Shield is rather... eh. It's easy enough to max out Smashing/Lethal Def without it. From everything I've heard, Dark Embrace is the best shield as it gives resists for four different damage types.
Group Fly with minions can be neat, too.
Also, if your going with Mercs, pick up two copies of the Achilles' Heel -Res Debuff for Soldiers and Spec Ops, helps compensate for Smashing/Lethal Resists being so common,
And, I'd recommend Burst instead of Slug, later on, they're both pretty useless except for carrying procs, and Burst recharges faster, meaning more shots at the procs activating. (Although, Slug can take the Force Feedback +Recharge proc)
Why are you lol-ing Serum?
Well, from what I can tell, I think IOs are much easier to get after 20 now with the new alignment merits.
Luck of the Gambler +Recharge, one of the most expensive recipes on the game (The last time I checked, which was a while ago, they went for about 175m on the market) costs about 2 alignment merits, according to the wiki.
__
@Eisenzahn
GW2 - Melchior.2135
AIM - Euroclydon23
Email - scorpany@yahoo.com or <sameasmyAIM>@aol.com (for the sheer novelty of an almost 20 year old email address that hasn't been overwhelmed by spambots yet)