I had a Tamagotchi, but it was the original Digimon toys that I was really obsessed with. I got my friend into it too so that I had someone to battle with. We were even raising them in class. We had all sorts of hypotheses about what made them stronger, which were probably based on no real evidence. I had a bulking-cutting strategy where I force fed my 'mon to increase its weight and then trained it until it reached the minimum weight for its rank.
I picked up an anniversary digivice a few years ago, I should replace the battery and raise some more digimon.