Mobility Enhancement Hybrid Thrusters (MEHTs)
Relatively straightforwards idea.
1. Weighs as much as I-JJs per tonnage class as per normal I-JJ construction rules.
2. Takes up the same number of critical slots as I-JJs as per normal I-JJ construction rules.
3. Can only mount a number of them equal to your walking speed, NOT your running speed, unlike I-JJs.
4. Any of them mounted in the legs, when in depth 1 water, cannot be used for jumping, but can jump a maximum distance equal to the number of them mounted in the torso.
5. Cannot be used for water movement while in Depth 1 water, only in Depth 2+ water. Cannot jump in Depth 2+ water (for obvious reasons).
6. Identical modifiers for jumping into or out of water, along with identical modifiers for jumping normally, or water movement.
7. Causes heat whenever used in EITHER mode, identical to normal jumping heat.
8. Conventional vehicles of any type cannot mount them (No we don't need that kind of insanity to an already insane game :) ). BattleMechs, IndustrialMechs, and ProtoMechs only.
9. Cannot be mounted on Super-Heavy 'Mechs of any kind.
Yes, Quad-legged units can mount them, in the torso and/or legs, with the same restrictions as I-JJs. Same with Tripods.
Personally, using these house rules, you can get some seriously awesome 'squid' 'Mechs to mess around with.
Optional rules/ideas:
Rather than being useless in Depth 1 water, each MEHT in a leg can be used like a single heat sink. So bipdel BattleMechs & IndustrialMechs get +2 to cooling, while Quads get +4, and Tripods get +3. To get this bonus, the unit MUST remain in Depth 1 water the entire turn (no 'touch and goes' type of shenanigans). Depth 0 does nothing as its too shallow for the MEHTs to properly circulate the water to get a cooling bonus.