Diamond Dude

Dude takes the cost away, you don't pay the cost if you hit a spell with Dude's effect.

Bonding H20 (You just special summon Water dragon because its a cost to tribute the monsters)
Destiny Draw (you just draw 2)
Trade In (You just draw 2)
Foolish Burial (Send monster to grave)
Monster Reborn (Summon a monster from either players grave)
Dark Hole (Destroy all monsters)
Feather of Phoenix (just add card from grave to the top of your deck, you do not discard)
Pot of Avarice (PoA has no cost, if you have 5 valid targets then you can use it and get your monsters back and draw 2)
Lightening Vortex (Destroy all face up monster your opponents control)
Smashing Ground (Destroy your opp monster with the highet def)

If the spell card has no cost then you can just activate the effect of it.

Confirming the nub above me.
Locked.