This battle takes place pretty much right after the battle with the Mind Guardian (either the Cloche or Luca version, depending on the route chosen), so it's advisable to use the Camp Circle outside the room of said boss in order to restore the party to full HP before going on. The ELMA-DSRX isn't as strong or powerful as the Mind Guardian, and almost all of its attacks are single-target ones, although it compenates this with most of them being multi-hitters: Tackle is a mere charge than hits a party member once; Stunray fires a beam that hits a party member three times and may inflict the Stun status; Slice Turn slashes a party member for three hits; Maximum Spin is a drill-like attack that hits a party member five times; Rolling Elma does something similar but for only three hits; and finally, Boost Cannon, which hits all party members once.
As for this battle the player will only have one Reyvateil available, they will have to be more careful, as one character won't be able to guard against attacks and the Burst Gauge will charge more slowly. Likewise, the erratic timing for all the attacks of the ELMA-DSRX will require the player to be more attentive than before to the Guard Gauge in order to block the attacks decently. However, the ELMA-DSRX doesn't have much HP, so a well-charged Pepen or Lady Momoyo (to around a 20000% Burst) will be enough to defeat it. This is more easily accomplished on the Luca Route, as Cloche will be part of the battle party and thus, the player will have access to Replekia. However, on the Cloche Route, the player will have to work harder to defeat it.
This battle isn't very different from the previous one, as the ELMA-DSRX didn't have any changes on its skillset except for the loss of Tackle, so if the player still has a good feel for how to block its attacks, they shouldn't have any problems winning. Likewise, the ELMA-DSRX has stats that aren't very far away from the enemies that appear on the area where it is located (the Cat Mansion), so if they could reach the place where the boss without any problem, defeating it should be easy as well. It must be noted, though, that it had a massive increase in elemental resistances, particularly against the Thunder element, so using Song Magic and attack items that have said property will only cause a pitiful damage against it. Therefore, it's a good idea to use non-elemental Songs, such as the ones recommended for the first battle.
ELMA-DSRX also appears as one of the enemies that must be fought in Jacqli's Cosmosphere, although it has been so weakened that the player should have no problems defeating it.