This loop relies on the constant, self-sustaining synergy between your creature types and counter generation. With Bloodline Pretender on the battlefield—having chosen "Wall" as its creature type—every time a Wall enters the battlefield, its triggered ability places a +1/+1 counter on it. That very act of putting a counter on another Hero then triggers Invisible Woman, Sue Storm, whose lifelink-enabled presence rewards you by creating a brand new 0/4 colorless Wall creature token with defender. Because this new token's arrival immediately feeds back into Bloodline Pretender, you get an endless chain of entering creatures, triggers, and counters.