5-8% Strength for 4.5s on Kill. Stacks 5 times.
Up to 5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
Your Grenades stick to Ogryns and Monstrosities. 6-15% Damage vs Ogryns and Monstrosities
1-4 Bleed Stacks from close range explosions.
The idea here is to combine tauntgryn and heavy hitter ogryn concepts with the firepower of flamy-explody-rumblergryn. Bombs Away could be more fun here but I think rock provides more consistent value and supliments the low ammo economy of Rumbler allowing to to be used more generously into mass and density.