My opening strat (erebus) is easy:
Priests... spawn them, attach one to my partner
Mana potion (it's pretty much all I can afford now that 900 gold is gone... but the priests and bite will keep the HP up, and the mana potion will keep the mana up, so I'm good for a while)
I use cloak of the night for mana, mana capacity, and for early and unexpected TP+bite attacks (and escapes).
I usually get my first kill at lvl 4 from a squishy ranged unit. People don't expect me to have TP yet and the bite at lvl 2 is considerably more powerful. Even when you hit lvl 5 bat swarm isn't a very good teleport since it uses most of your mana, often leaving you without the bite...