Summarize the following:
Do not recklessly attack Slade after mashing his mask off. He will be more dangerous than before, and he also won't let you attack him anymore. Any attempt to land a combo without countering will end up in a counter sequence beneficial to Slade only. Eventually, you will be able to land a few hits on him. Don't be too greedy with damaging Slade though. This battle is pretty long, and he isn't an easy opponent to beat, so it's better to conserve your HP. Once you've dealt enough damage, Slade will start using a gadget similar to the Batclaw. Once he fires it, it will attach to Batman's chest, and the other end will grab a canister of gas.  Use the counter button at the right time to send the canister flying at Slade. Quickly run up to Slade and attack him. If you fail to send the canister to Slade, he will start shooting at you with his gun, so try to send the canisters back as much as you can. When Slade’s HP reaches a certain low point, he'll once again throw a smoke pellet and attack you. This time, Batman will take Slade's staff and break it in half. In retaliation, Slade will now use his sword.

Summary:
Be cautious. Wait for the opportunity to strike, and keep countering and blocking Slade's attacks. Prepare to counter again. Continue countering and landing small attacks on Slade until you get his HP down. Counter Slade's strikes and deliver a beat down once you're allowed to.