Poisoning mechanic is too complicated, you need to at least vaguely mention it in the card without possibly referring to a simpler mechanic that currently exists (the skill "poison", give 1 counter to the opponent)
Plus, you lots of stuff worded wrong. The text should read:
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: Strangle
Kill the target smaller creature (less HP's). Python gains +0/+1. Poison your opponent.
But "Poison your opponent." still needs to be changed. I'd take out the HP gaining, and go with:

: Strangle
Kill the target smaller creature (less HP's). Poison your opponent depending on the target's HP's.
And remove the "(less HP's)" if necessary.