[quote=Tuco
- allowing more than one spell per turn in almost any circumstance (I think Action surge is the only real exception?)
The metamagic Twin is broken for those reasons.
According to the rules I can twin Haste, casting two leveled spells in one round, doubling the output of two martials, while concentrating on the 2 spells simultaneously.
I can twin Disintegrate and do 50-100 damage on two targets.
The metamagic twin is broken even with strictly applied D&D rules.[/quote]
Haste doesn't allow you to cast another spell - the description is pretty clear. As for attacks, you get +1 attack, not the regular attack action. Pretty sure what Larian is doing is simply doubling up on everything.
Also twinned spell is about extending a *single* spell - that targets *1* creature - to more targets. You are *NOT* concentrating on two spells in your haste example above - just as you aren't with the bless spell on multiple targets. So that is not broken at all and fits in the rules.
So you should not be able to use twin spell to cast 2 fireballs, which some are claiming.
Unless you can somehow (like AS) get another general action, that includes the 'cast spell action' you shouldn't be able to cast 2 spells around (except for a possible bonus action spell, but that has limits too, generally).
One can argue about whether Twin Spell is OP or not, but hat is a different discussion
