[Homebrew] Calculated Monster Stats

Currently in Unearthed Arcana (available as playtest content) are some neat new summon spells, such as Summon Fey Spirit (UA), which summon a creature whose stats are based on elements of the player summoning them.

The trouble with these is that there is no proper monster entry, meaning we can't pop them under Extras and keep track of them as for a wildshape, or other summoned creatures etc.

While I realise these are UA content and may not make into a final release in their present form (or at all), I think it would still be useful for the Monster system to be expanded to accommodate them. To that end the things we'd need would be:

• Calculated HP: Currently for monsters all we can do is specific a fixed amount and a rolled amount. What we need is the ability to set an amount per creature "level", composed of a fixed amount and one or more ability scores, this is then multiplied by the creature "level" (spell level for a summoning spell).
• Calculated AC: As for HP, the ability to set a base AC and some modifiers to calculate it, such as adding creature "level".
• Multiattack: The ability to have multiattack automatically added as a monster trait depending upon its level with a modifier. For example, the Fey Spirit's multiattack is spell level divided by 2, rounded down (so 1 at 3rd level, 2 at 4th etc.)
• Attack & Damage Bonuses: The ability to add the creature's "level" to its attack and/or damage rolls.

Combined with the ability to set a creature's current "level" in the Extras section we could then add it when summoned, set the correct level, and use the Extras section to track our new creature.

There are probably loads of other things that could do with being tied to creature "level", but the ability to produce calculated monster stat blocks would very handy, it could even be used to produce monsters that could be scaled up to make them more difficult (e.g- calculated challenge rating and XP), so you could still encounter elite versions of weaker monsters with a few clicks.