All Cast (5e Variant Rule)
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This rule is meant to be used to condense turn order, particularly with a bunch of spellcasters.
One player can invoke this rule on their turn by casting a spell that causes damage. Any number of players subsequent in turn order may choose to expend their turn and merge it into this invoking player's. So this is a useful rule for someone to jump to a higher rung in the turn order just to do one thing.
On the invoking player's turn, all the players who lose their later turns must also choose a spell to cast that causes damage. Thus, all the players who choose to merge their turn cast all their spells at once in the same turn. Certain effects may occur as a result of mixing so much magic together in a simultaneous stream ("Thanks to the acid stream, the electricity conducts and deals an additional 4d8 lightning damage", e.g.). The players then cannot make any other actions, bonus actions, or move until their next next turn.
An example of its use is as follows:
- Hylan invokes the rule and casts fireball.
- Georg and Ullen join on the turn. Georg casts ray of enfeeblement and Ullen casts lightning bolt.
- Cue rolls for attacks (spell attack rolls, saving throws, etc.)
- Spells conclude
- The round proceeds, skipping Georg and Ullen's turns in the order for this round.
- Next round goes as normal, restoring Georg and Ullen to the turn order.
This is a very erratic mechanic that is advised to use with caution. More so than utility, this rule is meant to give a feel of having a massive barrage of spells. DM's can replicate this due to a single round often having everything occur at once anyway. However, this does allow for some good storytelling when it comes to mixing and matching different spell effects. The DM can adjust it for spells that are utility and not meant for damage.