The material presented here is my original creation, intended for use with the OGRE system from Steve Jackson Games. This material is not official and is not endorsed by Steve Jackson Games.
Here's my personal take on how to get Ogrethulhu to be worth it's printed 300 VPs.
Ogrethulhu behaves as a standard Mark-V ogre in all cases not addressed below.
Ogrethulhu's Eye: Ogrethulhu has grown a huge eye on a tower stalk whose attack is the same as a laser turret (Attack strength two, no spillover, LLOS, doubled once to attack strength four in overruns, etc.) but with a range of 30 hexes and a defense of 3. This eye sits on top of a tower of defense strength 6. Destroying the tower destroys the eye as well. The eye can be regrown without regrowing the tower first, but the eye's range is only 10 hexes whenever the tower is unavailable.
Ogrethulhu's Pods: Ogrethulhu has six pods of defense strength two each on its flanks that have no direct attack but are used for spawning and so help with regeneration.
Ogrethulhu's Claws: Ogrethulhu's two claws have an attack strength of four, a range of four hexes and a defense strength of four each. These act exactly like main batteries except that they can attack at a longer range and have special powers in overruns noted below.
Ogrethulhu's Tentacles: Ogrethulhu has Six tentacles growing from its back. Each has an attack strength of three, a range of three hexes and a defense of three. These act exactly like secondary batteries except that they have a longer range.
Ogrethulhu's Tongues: Ogrethulhu has twelve mouths along its sides from which sticky tongues extend to gobble up infantry and other victims. The tongues work exactly like antipersonnel units and can only attack infantry and D0 armor units but anything that is destroyed by a pure tongue attack is considered to be eaten. Each tongue has an attack strength of one, a range of one hex and a defense strength of one. In addition tongues can shoot down cruise missiles that come within their range with a base roll of 12 each. (AP guns ought to have this same AA ability to help balance Ogres vs missiles.)
Ogrethulhu's Legs: Sixty units that work exactly like tread units (20 leg units per hex of movement), except that they work better in swamp than treads do. Ogrethulhu moves at half speed in swamp but it is never stuck and all non ram attacks against Ogrethulhu's Legs are at half strength (round down) while it is in a swamp. (It is "legs down" in the swamp. Note that this is in addition to the stealth bonus so you need to roll a six to score half your attack strength in leg damage.)
Ogrethulhu is very hard to hurt and even harder to kill. Due to its unearthly nature ordinary attacks are very difficult to target against it. Units that are in different hexes or more than one inch apart on the battlefield cannot combine their fire into a single attack on Ogrethulhu other than a Critical Hit, because somehow the angles of fire do not line up. In addition for every attack against Ogrethulhu subtract one from the roll and consult the normal CRT. (So on a one to one attack, you need to roll a 6 on the die to destroy the targeted system.) The only way to actually kill Ogrethulhu is to reduce it to negative 60 leg units. Yes, it can go down to (and recover from) negative leg units, but it cannot move until it has regrown all of these negative leg / life units and at least one normal leg unit. Blowing a cruise missile up on top of Ogrethulhu can do sufficient "leg" damage to kill it. (Especially if it's within the crater radius.)
Note that unlike the Ninja's stealth, Ogrethulhu's defense bonus even works against infantry overruns and shockwave attacks.
While it is at negative leg units Ogrethulhu can still choose whether to regenerate guns or legs, but once it reaches minus 60 leg units it is dead despite whatever else it may have. Note that it is possible to ram Ogrethulhu to death and its defense bonus does not help it against ram attacks.
If you are using the Critical Hit rules then Ogrethulhu's defense bonus is doubled against critical hits, giving it a total modifier against critical hits of minus three. (But a successful critical hit does kill it.)
During overruns Ogrethulhu may ram exactly as an Ogre Mark-V but it's claws have a special ability. Each overrun fire phase each undestroyed Claw may either fire normally (at doubled strength for being in an overrun) or grab any manned armor unit and eat it. (Survivors do not understand why their buddies just drove up to be grabbed by the claws and the Spawn aren't talking, or at least they don't say anything in any known human language.) All of Ogrethulhu's weapons do have doubled attack strength in overruns and all of its weapons work in underwater overruns, but only against submerged targets and only at normal strength (being doubled then halved).
If you are using the Ogre ram rules instead of the GEV overrun rules then Ogrethulhu eats without cost any armor unit it "rams" as long as it has a functioning claw and any infantry squads reduced by Ogrethulhu entering their hex are added to its gut.
Place those units consumed by a tongue attack (for infantry and D0 units) or claw grab (for armor in an overrun) off board in a area called "Ogrethulhu's gut".
Whenever Ogrethulhu enters a town hex roll one die. If the roll is less than or equal to the total of Ogrethulhu's undestroyed tongue units plus two for each undestroyed claw (so the total to roll against starts at 16) Ogrethulhu instantly eats that town hex and reduces it to rubble, before resolving any overrun. In addition to placing a rubble counter on the hex, place another one in Ogrethulhu's gut to trade in later for spawn. Note that Ogrethulhu can't help eating town hexes as it is always hungry. (In minis this effects a two inch by two inch square of town terrain each time.)
Finally, Ogrethulhu regrows destroyed parts. At the start of each of it's turns Ogrethulhu may indicate one damaged component to attempt to regenerate, roll one die and if the number rolled is greater than or equal to the defense strength of the targeted item it is repaired. For Example, a pod is regrown on a roll of 2 to 6. If rolling to regrow leg / life units, just roll one die and if the total is three or more Ogrethulhu recovers the amount rolled minus two in leg units. (So on a roll of 5 it recovers 3 leg units and on a roll of 1 it regrows none.) Ogrethulhu can never recover more of any item than its original undamaged state.
Roll an additional regeneration die for each pod that is about to generate spawn this turn. (So if all six pods are about to hatch, Ogrethulhu could conceivably regenerate seven times in a single turn.)
Also at the start of each turn after its regeneration roll, Ogrethulhu may start growing a Spawn Squad in each pod that isn't currently destroyed or already busy growing a spawn from the previous turn. Trade in two squads of eaten infantry from its gut for each Spawn Squad started. One rubble counter from an eaten town hex or six points of eaten armor units may be substituted for an eaten infantry squad. Note that a howitzer counter counts as 12 points and so can substitute for two squads of eaten infantry. The nutritional value of trucks and command posts varies with their point value in scenarios. The pod will then finish growing the squad at the start of Ogrethulhu's next turn if that pod is not destroyed in the meantime. This Spawn Squad will start stacked with Ogrethulhu but can move independently on the turn that it is placed. So if given enough chow, Ogrethulhu can spawn off 6 squads every other turn, if none of the pods are damaged.
2 Claws (Attack 4, Range 4 hexes, Defense 4) 00 6 Tentacles (Attack 3, Range 3 hexes, Defense 3) 000000 6 Pods (Defense 2) 000000 Eye (Attack 2, Range 10 hexes, Defense 3) 0 Tower (Defense 6, makes eye range 30 hexes) 0 12 Antipersonnel Tongues (Attack 1, Range 2", Defense 1, against inf and D0 only) 0000 0000 0000 60 Leg Units: Move starts at 3 hexes 00000 00000 00000 00000 (Movement drops to 2 hexes) 00000 00000 00000 00000 (Movement drops to 1 hex) 00000 00000 00000 00000 (Immobile, but not dead yet.) 60 Negative Leg / Life units (After removing all Leg units above.) 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 (Ogrethulhu dies)
Spawn Squad, Attack: 1, Range: 1 hex, Defense: 1, Move: 3 hexes.
Note that spawn do not combine into larger units than squads.
Like Ogrethulhu, subtract one from the die when attacking spawn. D or X results remove a spawn squad and they take spillover fire normally.
For example a GEV fires on a clear hex with three spawn in it. The first spawn takes a normal 2-1 attack and is killed on a roll of 3 or higher. The other two spawn take 1-1 spillover attacks and are killed on a roll of 6 each.
Otherwise spawn are treated as ordinary marine infantry (something aquatic about all those tentacles...) and have doubled attack strength in overrun and are subject to AP fire, etc.
Optional Rule: Heavy Weapons Spawn.
At the cost of twice as much chow as usual, Ogrethulhu may generate Heavy Weapons Spawn as the same rate as normal spawn. (I.e. four squads of eaten infantry, in one pod for two turns.) Heavy Weapons Spawn have the same attributes as normal spawn except that each squad of Heavy Weapons Spawn gets a single attack three range four hexes attack that is not doubled in overruns. Each squad of Heavy Weapons Spawn that participates to an overrun attack that destroys a missile tank or howitzer gets to rearm its missile attack from the destroyed vehicle.
The horror that Ogrethulhu inflicts causes different reactions in different observers, hence other rulesets exist to describe this nuclear armed madness.