Invasion percolation: always invade the boundary site with smallest random weight. The resulting cluster is fractal with dimension d_f ≈ 1.89 in 2D, equal to ordinary percolation.
IP without trapping: d_f ≈ 1.89 (= standard percolation). IP with trapping: d_f ≈ 1.82. The fractal dimension measured via box-counting N(r) ~ r^{-d_f} appears in the log-log plot.