Salvat 2005

Thundermare

Haste (This creature can attack and {T} as soon as it comes under your control.)
When this creature enters, tap all other creatures.

Its hooves strike lightning and the thunder follows quickly after.

Ninth Edition

Haste (This creature may attack the turn it comes under your control.)
When Thundermare comes into play, tap all other creatures.

Weatherlight

Thundermare is unaffected by summoning sickness.
When Thundermare comes into play, tap all other creatures.

Portal

Thundermare is unaffected by summoning sickness.
When Thundermare comes into play from your hand, tap all other creatures. (This includes your creatures.)