Bull Aurochs

Trample
Whenever this creature attacks, it gets +1/+0 until end of turn for each other attacking Aurochs.

Rukarumel, Biologist

As Rukarumel enters, choose a creature type.
Slivers you control and nontoken creatures you control are the chosen type in addition to their other creature types. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.
{3}, {T}: Create a 1/1 colorless Sliver creature token.

Aurochs

Aurochs Herd

Trample
When this creature enters, you may search your library for an Aurochs card, reveal it, put it into your hand, then shuffle.
Whenever this creature attacks, it gets +1/+0 until end of turn for each other attacking Aurochs.

Rimehorn Aurochs

Trample
Whenever this creature attacks, it gets +1/+0 until end of turn for each other attacking Aurochs.
{2}{S}: Target creature blocks target creature this turn if able. ({S} can be paid with one mana from a snow source.)