Dimir Tempo leans heavily on free countermagic (Force of Will, Daze) plus Thoughtseize to disrupt your combo. Defense Grid makes each spell cost {3} more except during its controller's turn, so on your turn their counterspells cost {3} more, including Force of Will and Daze when cast for their alternative costs. That makes it much harder for them to counter your key spells. Remember it taxes your own spells on their turn too, so plan to do your work on your turn. Veil of Summer stops Thoughtseize, Fatal Push, and Snuff Out from targeting you or your permanents, since all three are black. It also makes your spells uncounterable for the turn, which covers every counterspell they have, free ones like Force of Will and Daze included. It draws you a card if they have cast a blue or black spell that turn. Omniscience is too slow and clunky against a deck that disrupts your hand and pressures you with Moonshadow and Nethergoyf, so both copies come out. One Boseiju also comes out. Its Channel can hit Mishra's Bauble or a nonbasic land, but that does little against a tempo plan, and as a nonbasic land it is exposed to their Wasteland.