There is no definitive base sizes for the different monsters, use what fits.

The Old World is a vast and untamed placed where wild and monstrous creatures roam the dark forests and tall mountains. There are many creatures that are roughly human in appearance, though a little larger than a man, like Orcs, Trolls, and Minotaurs, but there are also bigger and more bizarre monsters in abundance: Griffons, Dragons, Manticores, and many more besides. It is with these large monsters that this section of the rules is concerned. Large monsters may be ridden to battle by mighty heroes and wizards. Many of these beasts must be hand reared by their master if they are ever to accept a rider, so the great leaders of the Old World pay vast sums to adventurers who collect eggs or hatchlings from the nests of Griffons and other winged monsters. This is a dangerous profession, and for many a fatal one, but it ensures that the Emperor's Zoo in Altdorf gains fresh creatures to rear on behalf of the nobles and wizard lords of the Empire. Large monsters are independent and powerful elements of the army. Some monsters develop loyalty and devotion to their masters and will fight for them willingly, while others are placed under enchantments or simply driven forward towards the enemy in the hope that they will attack the right side.

Monsters

Allow figures to fight the monster if it seems reasonable, the figures do not have to be in contact with the base.

If the rider of a monstrous creature is killed whilst flying up, then the monster will fly off and takes no further part in the game.

Assume all dragons are not subject to the Bound Monster Rules, but all other monsters not covered in the Beastiary are subject to them.

Warhammer Fantasy: 5th Edition

Monsters - Frequently Asked Questions
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What is the proper base size for the different monsters?
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What monsters are considered large and what monsters are not?
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Can only creatures in contact with the monster's 40mm x 40mm base be able to attack the monster?
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Are Giant Eagles considered large monsters and thus +1 to be hit?
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Does a Bat Swarm (flies 8") get to 'march-fly' 16"?
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Is the Wyvern's armour save modified by the attacker's strength?
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If characters riding monsters are slain during hand-to-hand combat whilst flying high then how is the monster reaction table interpreted?
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There are some monsters not listed in the new Battle Book Bestiary which appear in other books IE., Lammasu, Great Taurus, etc. Are they subject to the Bound rules (like say a Wyvren), or not Bound (like a Dragon)?
URL Copied!

Monsters - Frequently Asked QuestionsURL Copied!

What is the proper base size for the different monsters?URL Copied!

What monsters are considered large and what monsters are not?URL Copied!

Can only creatures in contact with the monster's 40mm x 40mm base be able to attack the monster?URL Copied!

Are Giant Eagles considered large monsters and thus +1 to be hit?URL Copied!

Does a Bat Swarm (flies 8") get to 'march-fly' 16"?URL Copied!

Is the Wyvern's armour save modified by the attacker's strength?URL Copied!

If characters riding monsters are slain during hand-to-hand combat whilst flying high then how is the monster reaction table interpreted?URL Copied!

There are some monsters not listed in the new Battle Book Bestiary which appear in other books IE., Lammasu, Great Taurus, etc. Are they subject to the Bound rules (like say a Wyvren), or not Bound (like a Dragon)?URL Copied!