From Dota 2 Wiki
This page is about cosmetic pets. For units summoned by hero abilities, see Summons.
Summoned Units or Pets are small companions that follow heroes around the map. They are purely cosmetic and have no effect on gameplay. Enemy players cannot see summoned units unless they have vision of its owner.
- Crystal Maiden's Frost Avalanche was the first to feature a pet-like companion, although it was not a separate cosmetic item.
- Removed the per-game pet limit.