Marco Po Road is the sixth stage in sub-chapter 20 of Stories of Legend, Silk Road.
The enemy base will spawn 1 continuous, clumped group of Doge, about 6 Doge Darks, and 5 Gabriels. If you waste a long time stalling the Doges, they will spawn Gabriels instead of Doge Darks. After a certain amount of time, the order will shuffle and the groups will be produced faster and faster at smaller intervals, and basic Doge groups will no longer spawn, replaced by Gabriels. After that, the only thing that they will summon will be Gabriels. If you stall for too long, the various Doge variants will increase in stats. After the enemy's castle health is dropped to or below 1,499,999 HP, Teacher Bun Bun will appear.
A useful strategy for this level would be to use cats with very strong area attacks or VERY high health, as the constant spawning of Doge Darks and Gabriels becomes very overwhelming if they are not killed quickly.
Lineup: Crazed Cat, Mohawk Cat, Crazed Wall Cat, Eraser Cat, Paris Cat, Crazed Sexy Legs Cat, Crazed UFO Cat, Drama Cats, Crazed Bahamut Cat, Ururun Cat. Spam stallers, and Crazed UFO Cat as soon as the battle starts, as you can't afford to lose ANY time. Don't worry, the Gabriels/Doge Darks give quite a lot of money. Remember to fire the cat cannon as Bun Bun appears, and don't forget to keep spamming despite the 'Can't deploy any more' message.
There is an easy way to exploit the stage. If you send a Li'l Giraffe or low leveled Lion Cat at the start of the battle, followed by Li'l Wall Cat spam. The spawned Doges would be blocked by the Giraffe and once the Wall Cats arrive, the Doges would not be knock backed by the Giraffe and would stay alive, allowing you to destroy their base by spamming the rest of your cats. Just don't use any long rangers and/or wave cats so you don't kill the doges behind the base, so this stage becomes a walk in the park.
This happens because of the enemy limit of the game, and the build up of the weaker doges, it "blocks" the stronger enemies from spawning, even the boss.