Here is a kumite exercise working on simultaneous block and counter strikes with a fast strike immediately after the block and a take down on the fourth combination. The attacker punches with a left kizami zuki (jab punch), the defender blocks and strikes simultaneously, soto uke (outsideblock) and gyaku zuki (reverse punch). The blocking hand can be closed or open. As soon as the reverse punch lands, immediately use the blocking arm to Strike uraken uchi (back fist strike) to the side of the neck or jaw. The second combination has the same attack kizami zuki (jab punch), followed by the same defence outside forearm block reverse punch. This time the blocking arm immediately strikes tettsui (bottom fist), the third combination is exactly the same with kizami zuki (jab punch) and a simultaneous block and counter punch. But this time the blocking arm strikes with shuto uchi (knife hand strike).
On the fourth and final combination the attacker attacks gyaku zuki jodan (reverse punch to the head), the Defender blocks uchi uke (inside block) with a left open hand or closed fist and counter at the same time with heito uchi (ridge hand strike) with the right hand.
When Marcus performs these combinations fast, he adds a guillotine choke after the back fist, bottom fist and knife hand strike. Then on the fourth combination he executes a takedown, try and use the left leg strongly along with the left blocking arm, which slams into the top of the opponents chest of throat, at the same time kick the left leg back.
This is a really good combination, working on speed striking and simultaneous block counters.
There are two more articles and videos that go with this one. The first video has these basic strikes put into a basic combination from shizentai (natural stance). The second video has these shotokan karate techniques in a kihon (basic) combination on the focus pads.