Formian Fugitives

Forsaken 2: Formian Fugitives gets -2/-2 when
any creature without Forsaken attacks alone.
Nightfall: Formian Fugitives gets +1/+1 and
Menace until end of turn (Nightfall triggers
Whenever a Swamp or mono-Black creature
enters the battlefield under your control.)
"Unsightly crossbred mutants, they are the lowest
Aelfatava:. Shunned for their ugliness of body and
soul. The flee to the UnderVast eagerly."