Flair, or Get smart
Think outside the box
Very fancy mechanics such as breaking the fourth wall happen during boss fights, such as the one with Psycho Mantis. In Wario Land and Wario Land II, the player has to break the wall of the level very often in order to collect coins or find a path to the end of the level. At first sight, this breaking the level could have a negative influence on the magic circle. But in practice, it just rewarded the player for thinking harder about exploration. It certainly did not give the level an impression of open-sandbox-world because the breaking could only happen once in a while, and not everywhere. But it added fun and rewarded the searching player nicely.
In fact, the feeling of a destroyable world was nearly never felt in the two games, except a few times such as during the Wario Land battle with boss Funfun.
In the first level of Wario Land II, the player can choose to stay asleep in doing nothing. This lets Wario sleep and opens a branching in the story. It took me quite much time to figure the way to unlock the alternate story branch, because doing nothing was not an intuitive way to solve a problem. But I found it very funny when I saw Wario concluding the level still sleeping (middle screenshot), while he is usually congratulating the player for the money and treasures he gathered (right screenshot). So it was not frustrating and somewhat rewarding to see this scene happen.
Monster infighting is tricking enemy monsters into fighting each other. It happens in Doom and (apparently) 70 other games. There is also a little trace of monster infighting in Wario Land, but it is more rewarded than in Doom. Mostly only Pouncers (heavy falling spiked cubes) and Pikkarikun (a cloud throwing lightning bolts) could turn other enemies (such as the small Pirate Gooms) into gold coins. Unlike Doom, there was a strategy for each of Pouncer and Pikkarikun to use them as "infighters". For Pouncer, the Gooms had to be thrown under it when it was up. For Pikkarikun, Wario had to be protected under a floor and a Goom had to pass between Wario and Pikkarikun.
The game design = learning design talk by Gee at FDG2010 is illustrated very often in the two games, but particularly well in Wario Land II. The Big Kamukamu (a fish) boss encounter, for instance, is a check that the player can make his/her avatar swim well enough to kill the boss.
As usual, most bosses strategies deal with dodging their attacks, finding their weak point(s) and attacking at the good time. Most have three phases, the third one killing the boss being the hardest and the most intense. However, there is a learning-by-the-example phase before two bosses: Awabo (a bubble) and Ghost. Before those two encounters, Wario sees Captain Syrup, the final boss, being imprisoned by the boss. It ignites a bit of schadenfreude from the player towards the Captain. However, the player is warned: the way Syrup is kicked out is what Wario must avoid when he fights.
Except throwing enemies, burping is the only ranged-attack (first on the left). Japanese version of Crazy Wario is actually Drunk Wario, and Penguins throw beer mugs (second). Surrealism (third). Typical Japanese TV entertainment color shades? (fourth)