Thank you for your opinions guys!! Replying by step:
1)Mirri: yes, true, sensei is better. In a meta without miracle I'd choose sensei with no doubts. But against it naming sensei with needle gives you a lot of tranquilllity. Mostly against mentor miracle, to avoid tons of monks in the battlefield. I know, no extra card and no trick with repeal.....basically the situation is this one:
PRO: open mana on upkeep/eot to look at your library, good vs needle/revoker, still scry, keep looking at your library against mentor
CONS: no extra card, no look at your library whenever you want, no tutor with trinket mage, green mana to cast, dies under decay/oblivion stone
I will buy another sensei and try it instead of mirri. My sideboard is weak against miracle if we don't consider needle, do you have any suggestion for this?
2) Sylvan library: if about mirri I can share your idea, I consider sylvan a strong must. Against a turn 1 chalice, this is a safety net. And, mostly, it gives us the possibility to draw extra card: if we are high with hit points (thanks to glimmerpost), this makes a big difference.
3) Exploration: in the past I didn't like it. It's true, after 3rd turn is useless, in GW build is a dead card after this turn. But whoa, if you have it on the first turns, it really makes a difference, against EVERY deck. Maybe the only matchup where exploration is critical is BUG/jund....exploration empties easly our hand, and so thoughtseize/tourach hit strong the remaining cards in hand. If we draw exploration on lage game, we can remove it from our hand with brain/fetch/maps. Crucible is a very interesting option, saving us also against wasteland, but it's hard to find a slot for it (and 1x is basically useless, since we cannot tutor it).
edit: the fact that after 3rd turn it is useless is not so true. Let's suppose that we start the game with a vesuva in hand and no cloudpost. We don't need to cast vesuva (unless other specific reason) early: but when we reach cloudpost, putting it into the battlefield together with vesuva is a nice surprise effect, that give also us a fast ramp. This happens also with "utility" lands: bojuka bog and chasm (sometimes tabernacle, if we are scared by wasteland, but in general I prefer a wasted tabernacle that cloudpost, it depends however.....) in general are useless in first turns: casting them after along with our base lands allows us to continue ramping and answering opponent's menace.
4) Explosives: I dislike this card. Against tokens, Tabernacle is much better. I tried explosives....if you remove 3/4 tokens against grixis or mentor, they easily put them in the battlefield again. With those decks you must hit pyromancers or mentors, not token. At least, with Tabernacle we slow them. Having more than 2 counters on explosives is VERY hard, we cannot rely on this to remove cmc 3 cards. Planeswalker? needle is the solution, no way. Wiping out battlefield? oblivion stone: grixis has delvers (0 cmc), shaman (1cmc), pyromancers (2cmc); bug has shaman (1cmc), tarmo (2cmc), liliana (3cmc); omnitell has....nothing XD; miracle has sensei (useless), mentor (3cmc), tokens(0cmc). Explosives are very very strong only against aggro loam, to remove chalices and mox. I can think to add 1 of them maybe, thanks to trinket mage, but no more.
5) Counters/spheres: mindbreak trap is good only against storm. But since that deck usually uses duress before comboing, I prefer to have something in the battlefield to slow/stop it. That's why I put 1 sphere of resistance....gaining 1 turn (2 cmc vs 3 for trini) can really makes the difference with storm. And in general with fast deck I think. Of course I cannot put 3 spheres of resistance 'cause I need trini with omnitell....
