Phyrexian Hydra

Oracle Text

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.

Card Rulings

6/1/2011 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.
6/1/2011 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.