DB6p100 the Enormous Tentacles of normal Demon Planets can reach 1000 miles, but it's unclear how fast they move, it's probably not 'instant' from the maw to the full reach so it may allow enemies to simply shoot at the tentacles from a distance when they're outstretched. They just need to keep in mind the necessity to withdraw if they enter within 1000 miles to attack the main body of the planet. Even if they're able to fly at Mach 10 like the planet, that'd be over 7 minutes to travel the distance. Even if the planet was moving toward an opponent as they launched the tentacles and you wanted to stack that to Mach 20, you're still looking at over 3 minutes to hit people at that barrier. There's mentions of 'Gravity Glands' you can destroy to free a 200 mile radius, but since these only generate 1 G I don't really get the point of doing that in star combat. Their 500 mile energy blast is a bit more impressive.
DB12p105 Cormal actually has gravity glands worth avoiding, reaching 250 000 miles (1250 times as far as a normal Demon Planet) and they actually have a described penalty (unlike Demon Planets, unless I missed something other than the 1 G) of preventing Star/Rift drives from working.
They can actually gravity-beam something within 125 000 miles. This seems like the main weapon of the Demon Fleet. I don't know of anything else to compare. The repulsor function I can't find a range for so I'm assuming it's also 125 000 miles.
Initially I did not know if Cormal had Enormous Tentacles like normal demon planets do. The MDC by location is listed differently and it seems like they might've been left out unless I'm not noticing it. The order is:
Demon Planets
Main Body
Enormous Tentacles
Nerve Clusters
Digestive Organs
Hearts
Brain Nodes
Gravity Gland
Blood Vessels
Major Artery
Epidermis
Cormal
Main Body
Brain Node
Gravity Glands
Organs
Nerve Clusters
Digestive Organs
Hearts
Blood Vessels
Major Artery
Epidermis
DB12p106 does mention under 'Enormous Maw Tentacles' that they are twice as long, so he should be able to attack up to 2000 miles with them. I guess I just don't know how much MDC they have? I guess maybe double due to 'twice as thick' or maybe quintuple based on organs all being 5x. Up to GM I guess.
Cormal can also energy-blast a 2000 miles as well. Castle Halthhag also has one with equal range on DB12p109 but only 1/3 the damage. Their 5000 mile range Cruise Missiles are more of a threat.
DB12p133 the Cruise Missiles of the Demon Fury Frigade can only reach 1000 miles, but have limited payload and can be shot down. Hell Fury missiles going Mach 15 for a full 8 minutes (per Pg137) would only be able to go 1522.414104 miles.
DB12p135 the Dark Energy Cannons of the Bone Maw Carrier can reach 200 miles, unlimited payload, can't be shot down.
Now: let's look a the top-tier of range for Mechanoids...
Trilogy page 95: Mother Ship: 52 000 kilometres plasma. That's 32,311.3 miles.
The Mechanoid Mothership is basically capable of defeating anything except Cormal.
Cormal v. Mothership would basically come down to: the Mothership is going to park far away (as its main unit is very slow, a meager 40 kmph unless they go to warp) and remove the Detachable Assault Unit and Planet Excavation Head Quarters (or DAUPEHQ). The main unit will try to stay say 500 thousand to 1 million miles away from Cormal, because if Cormal can get within 250 000 miles of them, they can no longer go to warp to escape and are screwed.
The DAUPEHQ will close in at a more agile 830kmph (515.738mph) and park 32 000 miles away and begin firing. Cormal will advance on the DAUPEHQ to get it in range of its more dangerous weapon systems. The DAUPEHQ will attempt to fly away to keep their distance advantage, however Cormal will hit it with a concentrated beam from a Gravity Gland to prevent its escape.
This then becomes a contest of: can the DAUPEHQ's plasma weapons destroy the gravity gland and escape before the gland draws it in range of Cormal's closer range weapons. I don't know how quickly Cormal's glands can draw things in though.
Make this assumption, not in Cormal's favor, and in favor of the Mechanoid mothership: the gravity gland doesn't draw them closer, the focused beam just holds them in place so Cormal can fly towards them at Mach 15 or 11 418.1058 mph. This would mean Cormal could get from the outermost range of the Mothership's plasma to melee range within 2.829830145732228194977839494183 hours or 169.78980874393369169867036965098 minutes or 679.15923497573476679468147860392 melee rounds. Let's round that up to 680 melee rounds.
The problem here: Cormal knows Impervious to Fire and Impervious to Energy and Invulnerability, all of which I think would make it and all its body parts (including its Gravity Glands) immune to the Plasma weapons of the DAUPEHQ. Plus, heck, even if this wasn't done, the plasma weapons don't do very much damage. Even if you converted SDC to directly to MDC, 6D6x30 isn't all that much.
Based on that, I think Cormal could definitely defeat the DAUPEHQ at which point, the core unit of the mothership is probably just going to hightail it to FTL before Cormal gets close enough to affect it with the Gravity Glands. So maybe a stalemate. Plus Cormal can heal damage and the Mechanoids would have to go to the effort of repairing it.
If we want an interesting scenario: have Cormal wake up and leave the Demon Fleet and go do his own thing. I think only Dominators and Robotech-tier space-ships are able to compete with Cormal's range, and even then, his ability to cast protective spells to protect himself are going to make hurting him implausible with energy weapons.
Mechanoids vs Fury Frigates and Maw Carriers would seem like more of a toss up.
Even a normal Demon Planet would know Impervious to Fire to counter the DAUPEHQ plasma weapons, but on the flip-side, they don't have Cormal's advanced gravity glands, so it would be plausible for the DAUPEHQ to withdraw from combat before getting in range of the DP's weapons. The DAUPEHQ is slower though, so they would have to retreat to the Mothership and re-attach to go to FTL in a prolonged chase.