Mario & Luigi: Partners in Time

Mario & Luigi: Partners in Time is a video game developed by AlphaDream and published by Nintendo for the Nintendo DS in 2005 in North America, Japan and China, in 2006 in Europe, United Kingdom and Austaria, and in 2010 in Korea. It's the second installment in the Mario & Luigi series.

It was re-released in 2015 for the Wii U's Virtual Console.

Plot
Mario and Luigi travel to the Mushroom Kingdom's past and team up with their infant selves to defeat the evil army of the Shroobs and their ruler and leader, Princess Shroob.

Why It's Timeless

 * 1) The story and plot is as interesting as Superstar Saga, and it even manages to be somewhat serious and creepy at times.
 * 2) You can play as four characters at once (those being the Mario Bros. and their younger selves).
 * 3) Lots of funny dialogue and good humor in general, as one would expect from a Mario game.
 * 4) Time travel is an interesting concept, and the songs that play during it are nothing short of ear candy.
 * 5) The four heroes can use unique Bros. Items and attacks, which are really original and useful to defeat bosses easily, like the Pocket Chomp, the Copy and Mix Flowers and the Trampoline.
 * 6) Several fun boss battles, including Bowser and Baby Bowser, Kamek, Shrooboid Brat and of course, Princess Shroob.
 * 7) There are some fun puzzle-oriented levels.
 * 8) Great animation and nice soundtrack by Yoko Shimomura, especially the boss, victory and the Bowser/Shrowser Battle themes.
 * 9) The L33T HAMM3R BROZ. are some of the most entertaining bosses in this game, especially due to their intentionally cringeworthy dialogue. They're also the ones to give the baby Mario Bros. their hammers as a retribution for freeing them from the Shroobs' mind control.
 * 10) Young and elder Toadsworth are a good spiritual successor to the Starshade Bros., as they teach the four Bros. special abilities to get farther into the game.
 * 11) Tons of likable characters, such as Kylie Koopa and Stuffwell (altough the latter is a little unfair to Luigi in a cutscene).
 * 12) Fawful, the secondary villain from Superstar Saga, makes a cameo. Granted, it may be kinda disappointing that he's the owner of the Bean Shop as opposed to an antagonist of any kind here, but he is as lunatically hilarious as ever. He even briefly references his loss against the Bros. (which he refers to as "brothers of badness") in the previous installment.
 * 13) The plot twist where Elder Princess Shroob is revealed to be trapped in the Cobalt Star is actually surprising.
 * 14) Mario and Luigi's voice lines are as amusing as ever, especially their new "BABIES!" line.

Bad Qualities

 * 1) Luigi (more especifically Adult Luigi) is frequently treated as a butt-monkey throughout the game, especially during the part that takes place in the Star Temple.
 * 2) This game is more linear than the previous game.
 * 3) Like Superstar Saga, there is no post-game content.
 * 4) The babies' crying is very loud and annoying. With the infamous being Baby Peach where she cries obnoxiously loud, especially when she cries due to Baby Bowser refusing the pilots to rescue adults Mario and Luigi.
 * 5) The boss battles can go on for too long.
 * 6) The final boss battle against Shrowser is very pointless, both story and gameplay-wise (mostly because The Marios and the Luigis can only rely on jumping or countering his attacks to damage him).
 * 7) Much like Cackletta's Soul from Superstar Saga, Elder Princess Shroob can be a huge pain.

Videos
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Hints

 * Make sure to have as many Bros. Items that have the Bros. jumping (eg.: Trampolines and Cannonballers or can reach a big height (eg.: Smash Eggs and Mix Flowers) for the final bosses (especially Elder Princess Shroob's second phase).
 * Ice Flowers can lower one or more enemy stats, making them good tools to hurry fights up.

Trivia
This is the only Mario & Luigi game prior to Dream Team to not have a remake.