Shockwave that is actually shaped like a wave radiating out from your character or the character's hands. It would ripple all around and hit anything not behind a wall or cover though it would logically even knock some walls and cover down or blast through them. That would be a true shockwave power. Come to think of it, shockwave would probably vibrate any object it it so it would still hit or damage things even in cover just with slightly less effect and it might reduce the range a bit.
Combat Drone; This one is shaped like an abomination but more mechanical synthetic looking. It would have some weapon like a m8 avenger and shoot it or it might have some power like throw or shockwave. Then it would fight any enemy it sees. It would make it a priority to protect the player that summoned it most and secondly any allies he or she has. It would last for the duration of a wave or at least half a wave before the need to summon again. Perhaps like, the Summoner game, it would drain the total hp and shields of the player that summoned it by a fraction so that there is a slight penalty to using it. UNLESS, the Geth Primes still get to keep their super powered 3 or 4 turrets and drones they can summon at once that are always there even after destroying them since there is no cool down time, they have more powerful weapons than even the prime in some cases, and appear always right by the players and never anywhere near the actual prime that called them. If that is the case, the player should get to summon a combat drone ONCE that lasts through the game unless destroyed then get instant recall. In fact they should also be able to summon up to 3 or 4 of them at once.
Cluster Multifrag Lift Grenades - yes it has the spread of multifrag, area of impact of cluster, and the damage of lift grenades. The best grenade power you could get. It would max out at 15. Somehow thermal ammo crates can resupply GRENADES a totally different type of ammunition than GUN BULLETS. Though the explosive grenade like rounds should also logically be a bit physically impossible as well. I suppose the internal gun shaver has grades of shaving to make rounds form .22 size up to 140 mm size and somehow add proximity fuses and a explosive chemical war head into the round. Wait, then it would not be simply a shaved bit of metal right? If it were hollowed out and filled with explosives?
Drell or Shadow type combat/melee training. Though they should be about the same with the drell logically being more like Jet Li unarmed combat martial arts superstar. In fact, change that to Drell Training and give him the martial arts combat skills he should actually have and the speed in combat he should be capable of mustering. This would include a high agility and ability to dodge power and weapon attacks with near superhuman agility and super senses. Since if he were actually a highly trained personal combat assassin specialist, he WOULD have such skills.
Krogan Sentinel fitness - they have the best shields, best melee damage but add Batarian heavy melee fitness attack and Vorcha regen ability. Then it would be the best fitness regimen. In previous games, all characters DID have some regen ability this actually makes sense. The only difference should be the rate of regen. Even though only the vorcha have it now, I guess somehow the Krogans and humans some how lost the technology between mass effect 2 and mass effect 3.