Spell Tank Bard & Shield Master

[kalebr]

The group I'm in consists of a Cleric (War), Warlock, Wizard & Rogue (Assassin). I created a bard, with the intent to go Lore, but based on the group needs, I decided to go Valor to help the group. With that decision, I'd like to make the character more of a spell wielding tank. Specifically, I'd like to use Shield Master with Cantrips to fight. Shield Master unfortunately states you can shove on a bonus action when you take the ATTACK action. Is there something inherently broken if attack action was expanded to include the CAST action? The DM is open to it and right now we have decided a melee spell attack will satisfy the attack condition, but I'd hate to find that we made a big mistake in allowing this at a later level.

Also, what suggestions for the build are there if Shield Master w/ Spell Attacks is allowed. Right now, I'm thinking of taking at least 3 levels of Warlock for Tomb cantrips ( Shocking Grasp, Eldritch Blast for ranged, Shillelagh for kicks ), short rest spell slots and some defensive spells (Mirror Image) from the Warlock list. I hope to make a "control" tank that's pretty defensive and versatile.

Finally, would you consider this 1 round sequence broken?
Shove prone with Shield Master, Dissonant Whispers to damage and create AoO at advantage since mob was prone.

[Sjappo]

Rule of Cool, I say let him do it. I'd let him use ranged attacks if you wanted to. Shoving prone and ranged attack is not that advantages IIRC. And shoving away is not very advantages for the other melee PCs.

If you want to curb this in somewhat you could have the Bard have a special variant which lets him shove and cast, not shove and attack.

[Shadow]

Just play a wardrummer. Ask him if you can have a set of small bongos and use a specially made mallet as a drumstick.
Now you're holding an instrument, which is your focus, and can use it as an improvised light hammer. And since you're proficient with simple weapons, and a light hammer is a simple weapon, giving your proficiency bonus on attacks with it as an improvised weapon is reasonable.

Bang.
Now you can cast and attack and have a shield all without needing a free hand, and it's all well within reason without needing to change anything. All it needs is the DM to agree that your choice of instrument used as an improvised weapon is close enough to a real weapon that you're proficient as to allow prof bonus on attacks.

I'd allow it.

[kalebr]

Just play a wardrummer. Ask him if you can have a set of small bongos and use a specially made mallet as a drumstick.

That's a cool suggestion. I intended to use Shillelagh to make a club into a CHA based weapon for attacks. Seems like I could have a shield that serves as a drum / gong which I play with my shillelagh club. Banging on shields for war seems ok.. I just do it with rhythm.

[Mrmox42]

That's a cool suggestion. I intended to use Shillelagh to make a club into a CHA based weapon for attacks. Seems like I could have a shield that serves as a drum / gong which I play with my shillelagh club. Banging on shields for war seems ok.. I just do it with rhythm.

This is brilliant. I am going to use this setup myself, now.

[Jlooney]

Can't you cast a cantrip as a bonus action? So shove them bonus action?