An ARTCC Controller reported confusion between video map display overlays while controlling an aircraft with malfunctioning navigation and deicing equipment resulted in descent below MVA and a CFIT event.

Narrative

Aircraft X was handed off and coordinated as a [priority handling] with no navigation no alt equipment and no deicing. It was coordinated that he was requesting the Rnav XX approach into ZZZ which I questioned because he didn't have navigation. I was then informed that he 'kind of' had navigation and he was requesting vectors. I asked what heading he was currently on and was told he wasn't on a heading just flying towards ZZZ somehow with his FMS? I said roger because obviously the other controller calling didn't have the full picture. Once he checked on frequency; I asked my own questions and discovered that he had gotten his navigation back and altitude readout but still no deicing equipment and was looking for a VFR hole to get through the cloud deck. I inquired some surrounding aircraft; and informed Aircraft X about a possible 'river' in the clouds that he could get through. I then informed him that a ZZZ departure routed 20 miles south of him picked up zero icing on the climb out but reported a solid layer at 10k that he could not see through. I vectored him towards the 'River' opening then gave him deviations left and right and Pilots discretion to 110; the bottom of my airspace. As he approached 110 I asked my supervisor if I should hand him off to ZZZ1 approach or hold onto him because he would eventually be handed back off to me once he turn back on course. I either didn't hear the response or there wasn't a quick enough answer so I made a command decision that with my 17 yrs of approach experience it would be a better service to limit freq changes and keep him on my freq since I knew the entirety of the situation. I pointed him out to ZZZ1 approach and continued his decent to 031 which was the lowest crossing alt on the RNAV XX app into ZZZ that he was requesting. I kept him updated with any knew information and remained in constant comms until he reached 031. Once he reached 031 I noticed he was turning back towards the IAF ZZZZZ and asked for an update; he told me he was still in the clouds and asked for lower; I descended him down to 026 which was the MVA and informed him that I could descend his to 024 in 2 or 3 minutes when he enters the next lower MVA or so I thought. Once i believed Aircraft X was in the next MVA I Descended him to 024; it immediately MSAW'ed but i thought well; i gave him lower right on the boundary of the 026 MVA that must be what the problem is. I gave him traffic on a VFR a/c right in front of him at 021 to assure him the bases were out there. I asked the CPC next to me for help and said am I reading the map wrong because of the MSAW. She told me to drop all map overlays which I did except for approach boundary's which there wasn't a quick button for. She told me where she thought the 024 boundary was; which was south of his position; immediately told him i busted the MVA and asked if he was in the clear; he said he broke out of the clouds at 024. i asked if he could maintain his own terrain and obstruction clearance which i knew the phraseology had nothing to do with the current situation but i figured it was something. Aircraft X then told me he could and he was in VMC conditions and that he couldn't take a climb back up because of fuel. I informed the next sector of the entire situation and handed him off for is app clearance into ZZZ which was 12 miles outside my airspace. In short I busted the MVA because 4 different map overlays all blend together and couldn't read them. I recommend to change the Map color for the MVA Map so you can differentiate between all the other maps.