Going by the list I sent above vs the populous decks on mtgg (and what I can think of), and please excuse my verbosity this is how I speak (and excuse me if I have anything wrong, this is based on my own testing and knowledge rather than others'):

Hammer Time (the mirror)
-4 Esper Sentinel
-4 Memnite
+3 Path to Exile
+2 Prismatic Ending
+1 Manriki-Gusari
+2 Seal of Cleansing

This mirror is weird; as usual mirrors are very practice-and-skill based but this mirror plays differently G1 to G2/3. In G1 you're very much racing your opponent, trying to get hits in before they do and using e.g. giver of runes to sneak in inkmoth nexus hits with hammer (often with flash using sigarda's aid). G2/G3, apart from outliers where you can clearly see a line to win, is all about Manriki-Gusari. If you have it and your opponent doesn't (in the 75) you're pretty favoured, but tutoring it with SFM (or gift - this is why I think Steelshaper's Gift is good in the mirror and mediocre elsewhere) is a good route to victory, and games with Gusari often go to "who gets their equipment killer active first". Also, remember, Protection from colorless from giver of runes makes equipment fall off. Oh, and pithing needle is really good here but don't name something you need to win from the situation you're in - if you're not sure, name Urza's Saga.

Burn
-4 Memnite (I often side out memnites
-3 Ornithopter
-1 Pithing Needle
-1 Springleaf Drum
+3 Path to Exile
+2 Prismatic Ending
+4 Sanctifier En-Vec

This matchup involves you leaning on either Shadowspear and/or En-Vec. Since Searing Blaze is so good against you, try and play around it (by e.g. not making unnecessary Urza's Saga golems) - same as Deflecting Palm, which comes up a lot more often these days. You can be patient, because they can't leave themselves unguarded either, especially if you have inkmoth + a free equip ability up (i.e. aid, since they can bolt paladin). One big lifegain swing from Shadowspear, or a few small ones, make these games a lot smoother - but this matchup is very much one where you're always playing "control". Also, the one ornithopter is kept in so you can fetch a creature (or sometimes a blocker) with urza's saga - which comes up more than you'd think.

Cascade Rhinos
-1 Pithing Needle
-4 Memnite
-2 Giver of Runes
+3 Path to Exile
+2 Prismatic Ending
+2 Void Mirror

This matchup is difficult and comes down to "surviving the rhinos long enough to make a big creature and stabilize". They run Fury now (usually, I keep losing to it in every deck that runs it) so be wary of that and don't overextend unnecessarily; Void Mirror is also a good card against them but it very much does not mean you are safe. They can just play a midrange game and outdo you because the adventure creatures (borrower/giant) were a mistake.They also usually board in force of vigor, so keep an eye for that. This might be your hardest matchup but you can just turn 2 them sometimes, and other times just stick to your plan of hammering them and it works.

UR/Grixis Ragavan+DRC decks
-4 Memnite
-3 Ornithopter
-2 Giver of Runes
+3 Path to Exile
+2 Prismatic Ending
+4 Sanctifier En-Vec

If you're confident they don't have EE, you can side out pithing needle instead of a giver, but they usually do (and often maindeck). You can definitely outgrind the izzet decks - especially with lurrus - but it gets a bit harder if they have lurrus too (and don't buy lurrus if you think you need it and expect hand attack). Letting ragavan hit you is less bad than in some matchups - hell, you can just take it sometimes - they're not going to even want to cast a puresteel paladin, even if they can. The one other note I'd have is that with bolt, unholy heat, and other cards (drown in the loch for example) I would always assume that mana open = removal available, more so than usual - unless you have to gamble. Chip damage is a lot here, and Sanctifier en-Vec is the best card in your 75. Oh, and Murktide is really good against you so save paths for that if you can.

4/5c Elementals
-4 Esper Sentinel
-1 Pithing Needle
+3 Path to Exile
+2 Prismatic Ending

If you can kill them early, do - because they'll outgrind you with risen reef and ephemerate stuff. Inkmoth Nexus is often your path to winning here, since their only instant speed removal is solitude and their only blocker for it is either endurance or vesperlark, so try and focus on getting sigarda's aid + hammer and flashing in a hammer after blockers (to preserve flying - this line comes up a lot so I thought I'd mention it here). Otherwise, this matchup is fairly typical in terms of magic - the only difference being their abundance of free spells. You can absolutely stick to your plan, be careful, and win this one though.

Tron
-4 Giver of Runes
-1 Cranial Plating
-2 Esper Sentinel
+2 Seal of Cleansing
+2 Void Mirror
+3 Path to Exile

Almost a free win - mulligan fairly aggressively for a t2-3 hammer kill (t2 requires a 0-drop, drum, nexus, aid and hammer) and you usually have about four turns to kill them (because even their t3 plays are not a problem usually). Paths are for Wurmcoils but you barely ever need them.

Living End
-4 Esper Sentinel
-1 Pithing Needle
-4 Memnite
+4 Sanctifier En-Vec
+2 Void Mirror
-3 Path to Exile

Your sideboard is so good here, but in game 1 you need to kill them before they get their cards off. Name Street Wraith blind with needle g1 and otherwise just regular play patterns; they can often t3 bring out two big creatures but if you're smart you can set up giver of runes and make it not matter (or make it so they have to block in certain ways). A later living end often results in too many creatures though. Sanctifier doesn't hit their blue cyclers (or their sideboard foundation breakers/ingot chewers which are a genuine problem I don't know how to solve yet) but is still powerful and turns their best plays (i.e. big living ends) into beatable midrange cards.

General control/midrange decks
-4 Ornithopter
+2 Prismatic Ending
+2 Seal of Cleansing
(find something for sanctifiers if they are colour-relevant - probably memnites - and cut something for manriki if they play stoneforge)

You can outgrind anything because the ways you grind involve lurrus, and making big constructs with sagas and beating down with them. Serra's Emissary is unbeatable G1 but you can side paths in to beat it - I have tried to find an answer to this (see brittle effigy) but I think you just have to accept it and not harm other matchups too much.(edited)

Other aggro (tribal etc)
+3 Path to Exile
+2 Prismatic Ending
-1 Pithing Needle
-4 Memnite
(sanctifiers if they're relevant, manriki if they play stoneforge)

You can outrace a lot of aggro decks (humans is fairly easy for example) and most of the games are fairly ad-hoc

Misc tips:

never play Urza's Saga on turn 1, even if you think it lets you advance and kill them quickly. If they interact it stops you using it to get back in the game by making a pair of constructs (often correct anyway) and you shouldn't keep saga-only hands anyway

Paradise Mantle doesn't work with creatures with summoning sickness but it does trigger Puresteel Paladin - this is the dilemma, but being able to fetch a mana source that also draws you a card (with Saga + Paladin) wins so many grindy games.

Activating nexus to pump constructs comes up a lot - at instant speed especially

You have a surprisingly large amount of mana in general so don't be afraid to crack silent clearings relatively liberally - but do try and make the most of urza's saga, the constructss get huge in this deck and you can use shadowspear on one to turn it into a game-ending threat quite easily. T3 saga into T5 two constructs, one with shadowspear, and swing for big numbers is a very common play pattern - and you can do this earlier with a combination of spear/stoneforge + sigarda's aid

Engineered Explosives is the best card in modern against you so if you expect it/can play around it, do so - pithing needle helps here too

speaking of pithing needle, if you aren't sure what to name in a specific matchup (especially g1s against things where you side it out) either name a relevant fetchland (i.e. arid mesa in burn) or mishra's bauble.