Vs Gravity

Gravity is the king of flippers. No matter what you do, it will always self right. The flipper is so powerful, however, that it can self right out of the arena.
Your best bet is to get around the high back section of Gravity. It does have weak armor, but you better have anti-flipper side skirts like Biohazard or Storm 2 to prevent Gravity from getting under you. It is the only robot to even lift Sir Killalot with ease.

Vs Son of Whyachi (US)

Son of Whyachi is an improvement over Whyachi, a superheavyweight robot that appeared in Battlebots US. It has a spinning three pronged propeller-like blade with meat tenderizers on it for high damage. It can easily get destroyed, and the Tribar(As the weapon is called) can be bent out of shape horribly. If you have a wedge, try and get under it, since it can't self-right.

Vs Biohazard (US)

Biohazard is one tough bot to crack. It has skirts and everything, including a srimech, but lacks skirt strength. Your best shot here is a powerful horizontal spinner, like Son Of Whyachi. (Mentioned Earlier) Biohazard has had some major trouble with horizontal spinners in the past, cause they collide with the skirts, and rip them off. Once you destroy the skirts, it's easy to destroy the armour and immobilize it.