Sydecka (サイデッカ Saidekka) is a big rhinoceros-like enemy robot in Mega Man 8 and Mega Man & Bass. Found mainly in the jungle levels (Search Man's stage and Burner Man's stage, respectively), and also in both of King's stages and Dr. Wily's stage in Mega Man & Bass, it can either launch missiles or other explosive weapons, or shoot its drill-like horn (it is invincible as it does this).
Strategy
Sydeckas have the highest amount of Health Points of any normal enemy in both games they appear in. Notably in Mega Man & Bass, it takes 60 normal shots to be defeated by Mega Man, more than double that of the average boss (28 HP), giving it the largest health pool of any enemy in the game after the King Tank, which has a total of 68 HP between its weak points. When playing as Bass, however, it takes 120 normal shots to be defeated, giving it the largest health pool of any enemy, not just in the game, but in the entire Mega Man series.
As such, especially in Mega Man & Bass, relying on the Mega Buster or Bass Buster to take a Sydecka down will take incredibly long, so utilizing one of its multiple weaknesses is a far better strategy. Fortunately in Mega Man & Bass, at least one of its weaknesses — the Ice Wall — will have already been unlocked before it is even encountered for the first time in Burner Man's stage, since defeating Cold Man is required to unlock the stage in the first place.
Etymology
Its name is probably a combination of Japanese words, "sai" (サイ, rhinoceros) and "dekkai" (でっかい, big).