Wyrm has the following text:
1[Credit]: Ice has -1 strength.
Parasite has the following text:
Host ice has -1 strength for each virus counter on Parasite and is trashed if its strength is 0 or less.
If I understand this correctly, if I place a Parasite card on an ICe's, and use Wyrm's (somewhat expensive) ability to lower an ICe's strength, I can bring it down to 0 and then Parasite will kick in and kill it. Am I missing something?
Yes, this combo works.
Parasite will trash any ice as soon as it has zero (or lower) strength, regardless of how that strength was lowered (i.e. it doesn't only trigger from Parasite's counters).
Other cards that combo with Parasite include Datasucker:
Whenever you make a successful run on a central server, place 1 virus counter on Datasucker. Hosted virus counter: Rezzed piece of ice currently being encountered has -1 strength until the end of the encounter.
or Ice Carver:
All ice is encountered with its strength lowered by 1.
