Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
If damage would be dealt to Phyrexian Hydra, prevent that damage. Put a -1/-1 counter on Phyrexian Hydra for each 1 damage prevented this way.
If damage dealt to Phyrexian Hydra can’t be prevented (due to Leyline of Punishment, for example), it will be dealt as normal and won’t cause Phyrexian Hydra to put -1/-1 counters on itself.
If multiple damage prevention effects, including Phyrexian Hydra’s, are attempting to prevent damage that would be dealt to Phyrexian Hydra, its controller chooses which to apply.