Damage - Holy god the damage, the sweet, sweet damage
Healing - Actually not a bad healer all things considered
Revenant - Can be revived by angel dragon, which is very good news
Physical attacks and skills
Fetch - Unicorgi's first skill is possibly her least impressive. It does solid slashing damage to all foes in front of her. It's not bad, but neither is it amazing.
Grab That Tail - Immediately, we go to her most powerful skill. This skill turns Unicorgi into a miniature buzz saw for 3 seconds. The damage listed is done repeatedly to nearby targets. I don't know how many hits it does simply because targets rarely live through the full 3 seconds. On top of all that, Unicorgi is immune to physical damage while this skill is active, making it very hard to stop. My vote for one of the best physical skills in the game.
Nyandog - Unicrogi's healing skill. The base number isn't that high, but it heals all allies which is somewhat rare in this game. You're not going to get Faith Healer or Angel Dragon level healing out of this, but it's a welcome addition to her kit.
Paw Power - A passive skill that boosts Unicorgi's Agility. For anyone new, Agility is your physical attack stat in this game. So this passive boosts the strength of all of Unicorgi's physical attacks (and since she has no magical attacks, it's pretty much all of them).
Weaponized Cuteness - Unicorgi's legendary is probably the first legendary that I can say is just as effective at level 1 as it is at max level. This skill comes in 2 parts. The first is that all damage from heavy opponents is reduced by 50%, this is a flat rate and the most useful part of the skill. The second part is that after Grab that Tail anything that survives has a chance of being charmed for a few seconds. This part of the skill rarely works, and when it does, all it does is stop them from attacking for a short time. You can leave this at level 1 and keep the heavy damage reduction and have it work just as well.
Flame runes, flame runes, flame runes. Nearly all Unicorgi's essential skills are based off physical damage, so you want it as high as possible. There is also an argument for a tank set (tree, mist, rock) to keep her alive longer, but in my experience you'll get more mileage out of a high damage set. Since her white is nothing special you can avoid river runes, and you can use bolt if you prefer over flame.
Brozerker - Unicrogi needs shielding, bro needs some offense, both of them can heal, a good pair.
Bardbarian - Like all attackers, corgi appreciates a speed boost
Angel Dragon - Normally don't try to add Angel, but Unicorgi has a tendency to die, so the resurrection is very useful
Ninja Dwarf - Ninja provides a distraction and is tanky enough to give Corgi some space to operate, and Ninja appreciates the heal.
Plant Soul - A better bodyguard than Brozerker, but if in auto you cant' guarantee that Unicorgi will be the one that's protected
Vile Bile - Another bodyguard, who appreciates the heals.
Spectral Drake - Spectral is immune to physical... so guess who's totally out of luck?
Silent Spirit - His wall can block corgi's attacks, tea time can heal the damage, and Spirit isn't heavy so no damage reduction.
Bardbarian - Bard can speed everyone up fast enough to take corgi out before she can attack
Plague Mogul - One swing of the scythe should be enough to take corgi out
Master Thief - Misdirection returns damage, chase that tail deals a crapton of damage. This can equal a team wipe if you're unlucky.
Kraken Lord - The Horror reduces your already low armor, and Stand Back reduces your speed.
Faith Healer - His passives reduce your damage by a sizeable amount and he can heal up any damage you do manage to do pretty fast.
(+) Staggering physical damage
(+) Moderate healing ability
(+) Multiple hits make it easier to break down barriers
(+) Since everything is physical, you're able to score life steal on all hits
(-) Terrible defenses, rarely able to take multiple hits
(-) If the target nulls physical attacks you are out of luck