Super Robot Wars MX (スーパーロボット大戦MX Sūpā Robotto Taisen Emu Ekkusu) is a video game for the PlayStation 2 that was later ported to the PlayStation Portable with minor gameplay tweaks and titled Super Robot Wars MX Portable.
MX is also one of the few games in the franchise where the player does not have a choice of which "Banpresto Original" protagonist they can play. In this game, both original characters, Hugo Medio and Aqua Centolm, share the same machine, though there is still a choice of which two mechs to use: the super robot Garmraid or the real robot Cerberus.
Another notable change in MX is the Mobile Suit Gundam series do not partake in any of the major events of the game. Other than G Gundam, which loosely links their endings (from which the MX storyline is set after the endings, according to the events of Super Robot Wars Impact) and plots to the "Banpresto Original" storyline, the other Gundam productions almost solely exist in purpose to support the other non-Gundam titles of MX. It departs from other Super Robot Wars productions where conflicts between various Gundam factions must be taken as part of the overarching storyline. The only other game where a Gundam entry does not take a main role is Super Robot Wars W for the Nintendo DS and Super Robot Wars NEO from Wii.
Because of the series included in MX, it is often theorized the game was intended to be a direct sequel to Super Robot Wars Impact, since it includes several of the same series from that game, most notably Machine Robo. At the same time, both games feature the "Free Route" system: instead of following a completely linear progression, the player is able to choose what order to play certain scenarios in, potentially affecting the storyline or giving the opportunity to receive hidden units or characters. Additionally, MX and Impact use the same in-game font, and much of MX's soundtrack is remixed or rearranged from Impact's (a remixed version of the Impact theme is played in the final stages of the game, further supporting the theory). Some sprites and cut-ins from Impact are reused in MX; the most noticeable is arguably the God Gundam's sprite and the "God Finger" attack cut-in.
Source: Wikipedia, "Super Robot Wars MX", available under the CC-BY-SA License.