Battleaxe - Spend maybe 1 or 2 upgrade points to buy. It has a longer reach than the energy sword, but a slower swing time. Could unbalance enemies without having the unbalance perk.
War hammer - Again cost maybe 1 or 2 upgrade points. Has an even longer range but an even slower swing time. Unbalance enemies further and for longer?
Duel Arrows - Being able to fire two arrows at once? Maybe having a choice of the 300% width arrow, or two 200% arrows that were less accurate? (Cost same energy as one arrow) ((if you buy one option you cant buy the other))
Armour - I think the worst feeling is getting into a high round in titanium and then having one block of your hand cut off and dying... so many implementing buying Armour at the upgrade bot. If not full body armour, you could maybe have to buy a helmet, leg armour and then body armour? Just giving a little more protection and maybe stopping one sword strike and one arrow? (would help with being shot in the back by an unlucky arrow deflected by the mark 3 swordsman) xD
Shield - Buy at upgrade bot for 1 point. Hold in robots left hand and can hold up shield with the rmb. It would disable you from swinging your sword on the left to right side. It would block sword strikes (maybe if the enemies had battleaxes or warhammers the shield would break or you would be stunned)?. It could also block arrows. You could make it so you had the choice of whether to buy the shield and be able to block sword strikes and block arrows, or the deflect arrows perks, being able to block swords less reliably or be stunned more easily, but be able to deflect the arrows back. (Again if you bought one, you wouldnt be able to buy the other)
Drone - A circular flying ball with a red eye (weakspot) that would fire arrows at you. it would appear in the silver or gold tier and the commentators would tell you that you would need a bow, or have to use jump pads to kill it.
Boss - Having an enormous robot wielding an execution style battleaxe or a massive warhammer would be amazing. Maybe appearing in the level 20 titanium, or in the story mode as a last level boss. It would have multiple weakspots like spidertron.
I hope you like my suggestions, I love this game and I cant wait to see what you do with it! Thanks!