Age of Sigmar/Tactics/Monstrous Arcanum
Forge World monsters of all kinds and sizes. Some of these are more or less part of another army, because they have the relevant keyword (Dread Saurian is a Seraphon, for example), but others are kinda their own thing. These creatures don't share a common keyword, so there's no incentive to play them together, unless you want to make a tematic Monster army or something.
Warscrolls
Behemots
Basilisk: Fast, fragile, and nothing to write home about in melee. But it has an awesome ranged attack. Keep him close to the enemy, but well protected, and it'll do wonders.
Bonegrinder Giant: A king-sized Giant, with a powerful but inaccurate ranged attack, and good armor (4+). Quite fast and powerful overall. Otherwise a pretty vanilla Monster.
Brood Horror: A pretty lame at everything giant rat. It's a Skaven Moulder, so you can buff it with some minis, but very unremarkable and ability-less overall.
Carmine Dragon: The dragon every guy dreams about. Very hardy at 14 wounds and 3+ armor, with Chaos Warrior-like save of 5+ against mortal wounds, also hella fast. It can unbind spells and heal itself while doing it, and everything within 6" of him gets -1 Bravery. But it also shoots blasts of pure Death magic, dealing D6 + target Bravery - D6 + Carmine Dragon's Bravery (10, just great). Oh, and you re-roll the dice against Death and Daemons things (the ones with Bravery 10), so it isn't useless against them. With the -1 to Bravery of close units and its Bravery 10, you can easily deal 4-5 mortal wounds for each shoot, just awesome. Use this dragon with bravery-reducing sheanigans, but remember it's an Order creature itself, so plan accordingly so your army doesn't lose the Order allegiance. Or lose it anyway, because this dragon is awesome enough to make it worth.
Colossal Squig: Random and not very durable, but fast and scary as hell. Keep it far from your other units, because it might eat them up; send it to the enemy lines asap. It's a Moonclan unit, so buff it and start the massacre.
Curs'd Ettin: Pretty fast, but badly armored, and not killy enough. A litte lame, but it's a Mortal Chaos unit, so you can make it better with some Slaves of Darkness things. But you can't give him a Chaos Mark, so it'll never be truly useful.
Dread Maw:
Dread Saurian:
Fimir Warriors:
Incarnate Elemental of Beasts:
Incarnate Elmental of Fire:
Magma Dragon:
Merwyrm:
Mourngul:
Preyton:
Rogue Idol of Gork (or possibily Mork):
Skaven warlord on Brood Horror:
Skin wolves:
Squig Gobba:
Troll Hag:
Warpfire Dragon:
Wolf Rats: