I'm trying to cut down the size of my collection and storage space needs, while maximizing the variety of cool models I have to paint and the lists I can play. To get more 'bang for my buck' I’m planning on having a lot of armies including allied models, that I can use under multiple army lists as counts as proxies for their troops - meaning I can have a variety of cool models without going overboard on numbers/storage space.

Some of you may do similar or have comments and ideas of your own so I thought I’d share possibilities I’ve thought of (in no particular order):

Skipping the actual Battle Sisters lists, but collecting one single mixed formation of all the different types of Battle Sisters that could count as a mounted guard or skitiarii formation (all sisters = troopers; rhinos/repressors/immolators = skitiarii rhinos or ig chimeras; exorcists = hydras).

Collecting 2/3 Death Korps and 1/3 Ad-Mech troopers that can count as DKoK or Ad-Mech, plus also IG and tank lists. Both DKoK and Ad-Mech are the only army lists currently to use include Gorgons and Machariuses allowing for good cross-overs. I plan to base my DKoK artillery on a big-ish base with space for a Trojan on, but not having the Trojan glued on (with thanks to Man of Kent for this idea). If I want to count it as the equivalent mobile artillery in an IG list I can just place the Trojan on the base and/or in contact with the artillery and count the whole thing as one single Basilisk/Hydra. I may count then Medusa platforms as Bombards, since the EpicA stats inaccurately have the Bombard as a similarly short ranged vehicle. New-style Bombards could then count as Manticores, since the W40k stats (and the stats from older editions of epic) had it as extremely long ranged artillery.

Collecting a big ork army that can proxy as Orks, Feral Orks, OGBM and SF. I only plan to keep around 1.5k of Feral Orks, but still have a perfectly usable list for normal games by proxying bikerz = boarboyz; squig catapults = big gunz; supa-stompaz = steam gargant; larger gargants = Orkeosaurus. The last one is rather a stretch, but you could imagine a truescale Gargant could potentially have a transport capacity similar to a battlefortress if it cut down on guns a bit. I might have to claim / rationalize the Gargants had recently fought in a very long engagement and had run low/out of ammo for their bigger weapons though.

Space Marines counting as Chaos Space Marines could be done easily enough.

LaTD could proxy as Vraksians or IG. A few cult units/models could count as other god’s units in god specific lists I reckon. I’m probably going to use the odd Ad-Mech formation as undivided Dark Mechanicus cultists too.

I’ve yet to look through the Dark Eldar units or think it over but maybe it could be feasible to proxy Eldar units as Dark Eldar in a combined army to play as either? The upcoming Forge World book features Eldar Corsairs, which I gather will have an army list where they field a mix of craftworld elder units and dark elder units, so there’s background support for mixing the two in one army.