I don't know if there is an extra skill, let me know if there is any:
Swap, cost 800 gold and you need to use it in two towers to swap position. I have no idea if you can level it, nor the effect of such leveling.
Aim: cost 200 gold last 5 minutes and gives 600/900/1200/1500 range.
Burst shot: Cost 200 gold, it lasts 30 seconds altough it says it lasts 60, and gives 80/120/160/200 increased attack speed.
Coup of grace?: Cost 200 gold, lasts 60 seconds? and gives 10%? of chance of critical x4, x6, x8 or x10
Gem skill, gives 40/55/70/85 increased chance to gem an specific gem type in the next tower you place. I don't know exactly how it works, but if it works like I think, with the level 4 skill the 85% increased chances make it 97.5% of getting that specific gem.
Enchan Heal: cost 500 gold and cures the gem for 1-5/8/11/14 hp
Puck: Cost ¿500 gold? last 30 seconds and gives 10/15/20/25 % chance to elude something.
Omni: Cost ¿500 gold? last 30 seconds and absorbs 1/2/3/4 of the damage each unit does to the throne.
I think that these are all skills and this patch didn't add anything.
It would be nice to have a legendary skill that improves for 1 tower the chances to get better gems, getting opal/sapphire 6 can be tricky even with death's prophet/crystal skill