Amoeboid Changeling

All Sliver creatures get +2/+2.

All Sliver creatures have "2: This creature gets +1/+0 until end of turn."

This land enters tapped with two charge counters on it. T: Add G. T, Remove a charge counter from this land: Add one mana of any color.

Choose a creature type. Draw a card for each permanent you control of that type.

All Slivers have shroud. (They can't be the targets of spells or abilities.)

T: Add one mana of any color. Spend this mana only to cast a creature spell.

(T: Add G.)

Each Sliver card in each player's hand has slivercycling 3. Slivercycling 3 (3, Discard this card: Search your library for a Sliver card, reveal it, put it into your hand, then shuffle.)