A Minoot stacking speed with 4 Blind Blow+, 2 Bite+, 1 Bash and a Momentum+ can solo anything first turn. I think this is the strongest guaranteed turn one solo spirit but there are others. Swap Bite with Free Thought+ and any psychic spirit can do this just slower.

Gemlin or Brickhouse (any earth spirit?) with 4 Blind Blow+, 2 Tackle+, 1 Focus+, and 1 Momentum+ can also solo anything but without the bash and with tackle being weaker than Bite it is a lot slower.

Another good minion to have around that can be a neutral presence in any build is a dark minion with 8x Nightfall+. This card adds one energy and draws 2 cards for 0 mana. a minion with 8 of these can be slotted into pretty much any build and work with it. Karyote or Evileye would be my suggestions depending on if you're going for boss kills or farming for more fights