Note on Parasite and Toadfish:
Parasite: fragile creature, slow CC.
Toadfish: Trio if using this, good luck with quanta balancing.
1 damage for every 2 is a good balance. You'll have to have 10 counter to break even with Lightning.
If this is the case, it could use cost reduction too. 2
| 1
is good enough.
(actually if you want to go with 1:1 ratio, 3
| 2
could be just fine, but i suggest the damage : poison ratio to be no higher than 1)
Question: why don't you make it so that it deals damage based on opponent's poison counter instead of yours? It could be more of poison support card rather than poison deck counter (no pun intended)
EDIT: ninja update. Let's see if this post could still be useful.