There are already great videos about rune shops, and here I won't bother to re-introduce strategies/tips touched by them.
Plectro's great videos about rune shops.
Overview, Tier1: https://youtu.be/gokM1vbgaQU
Tier2: https://youtu.be/ej6kmKld2YU
Tier3, SSS: https://youtu.be/QQKG0_m0eA4
Hokuho's awesome video about score race strats, which includes safe kills for bloodshop.
[General]
If you attack blood/glass shopkeeper with axe/cat/rapier's move-attack, his teleport happens before your move, which can insta-kill you (unless you have pain ring, which goes after move, or war ring, which knockbacks him).
Conjurer, Pawnbroker and Glass/Blood(/Food) Shopkeeper have convenient wall torches for infernal torch + blooddig kill.
[Shriner]
If you place a bomb and immediately get out of shriner, you'll get teleported back to shriner fight.
Shriner doesn't spawn pain/sacrifice/chance shrine, and if all shrines are already shown up, it spawns glass shrine instead (which sometimes force Aria/Coda shriner to have 2+ glass shirne).
[Arena]
You can steal arena's items without starting an arena fight with shadow ring, but except rings (picking ring will start the fight).
On score run, you don't want to summon a lep in arena (to get full lep gold). On most of characters, you can pick up the pile. On Monk, you can just drop a beat to prevent it. On Coda, you still safely can drop a beat with iframe-double tap. If you have earth, you can use it to make a lep trap in arena too.
On score run, you can blooddigging/bombing wall wisely before the arena fight to make dragon/nightmare dig remaining walls.
Fight will be activated even after bombing items.
Items are from red-purple-black.
[Conjurer]
Conjurer places items in this order (get blocked by familiars). If all of #1~#12 are filled, conjurer places everything on #1.
If you step into #4~#6 with a ring on it, you pick the ring, then conjure. If you do this with shadow ring equipped, you spend moneys to conjure if you have enough (otherwise just ring swap happens). This can ruin your score run.
Shadow conjure can be messy, and you can spend your bomb to avoid/mitigate it.
You can't become rich by conjuring items with negative prices (after overflow). It will just make conjure free, or bankrupt you (except Mac single zones). See here.
[Glass]
On Bolt/Coda, you can use pause buffer to kill glass shopkeeper more easily. Pause buffer itself is a controversial tech, but pause buffer kill for glass shopkeeper seems exceptionally accepted by the community (?). (Disclaimer: Personally I don't do it.)
On Aria, throw-kill is consistent if you have potion or any protection (you lose them if it's bad teleport). If you want to save your potion for bad teleport (or your life if you don't have it), you can buy glass armor beforehand.
[Blood]
When you kill the blood shopkeeper, you don't need to go around food when you'll pick blood drum anyway. You can buy it and eat it during the fight.
Left item is always a gold weapon.
You can buy center item then throw, in case of right-teleport (left-teleport too if right item is also a weapon) assuming you can afford to buy 2 items.
[Transmog]
You can remove your equipment by transmogging (and not touching new one), which can be useful to remove your torch when you accidentally picked with darkness active.
You can kill transmogrifier to get a transmute scroll, especially when your last transmog granted you dry baby and your money ran out.
There are a lot of ways to kill transmogrifier besides the strats here.
Sometimes you encounter "Transmog Failed!" (and success afterwards) when you have enough money, especially on Aria/Coda. Explanation can be found here.
There can be a transmute scroll under the transmogrifier (with a small chance). Explanation can be found here.
[Foodshop]
On Bard, if you mash too hard to kill food shopkeeper, he won't die and will chase/kill you.
Rumor says it's actually health shop.
[Pawnbroker]
Sell price is 0.5x of CoinCost, which is 1/5 of Z1 price. Crown of greed won't affect price. Charisma makes it 2x.
You can use dove familiar to teleport him after aggro (as well as other rune shopkeepers), which can be useful on duping score (especially important on Bard).
[SSS]
You can kill SSS with bomb + greater fireball with frame-perfect(?) input. See here.
When you want to activate middle shrine and bombing side shrine, you can use red dragon's breath to kill shriner to make it free (especially if you don't have money).
When you want to activate middle uncertainty/blood shrine and bomb side shrine, you can throw-kill shriner to make it free.
Throw-kill itself is available for all shriner, and sometimes you do it even if it's not middle uncertainty/blood (ex. to get cap from space with 1 bomb no coin, or when side uncertainty/blood with no bomb no coin).
You can keep multiplier for obsidian weapon by throw prep.
You can use lunging to conjure/transmog head/ring 4 beats faster, and armor/shovel 1 beat faster.
Especially useful with shadow ring.
You can use transmogrifier's position to transmog shovel without bombing a wall, and you also can use bomb to get money for transmog when you don't have enough money.
For sub/low4~ you usually buy bloodshop instead of kill.
On Bard score, you can shadow conjure as many weapons as possible and scatter them all over the floor via throw/swap. Then you can cast greater transmute to get almost everything you want.
Theoretically you can consistently kill glass shopkeeper with 1 bomb, but it needs quick reactions against his teleport.
You can try to use double bomb to avoid/mitigate these reactions. Probably you want to/can switch to normal fight when you get bad teleport.
You need to place the 2nd bomb in late beat, otherwise bomb will be placed outside.
You can also buy 1 item then place a bomb below glass shopkeeper. This is 100% consistent at the cost of another 1 item, but you still get a glass jaw. (I learned this from DLKurosh.)
For safe kill on Coda.
You need to throw the 2nd grenade in late beat, otherwise grenade will be placed outside.
I learned this from DLKurosh.
Sometimes you need to wait few beats to re-enter, depends on his teleport.
Shield slot makes throw kill safe. (Face bloodkeeper to consume shield -> iframe through) (Sometimes you still need to buy the center item.)
video: https://discord.com/channels/83287148966449152/83287148966449152/1011551673824583690
You can generate head equipment from nothing via transmog in bat form. (If you already have them in slot, transmog will just normally change it.)
I learned this from a race against biggiemac42.
This increase the number of items. You can kill transmoglifier for transmute scroll, and use it for them.
If you have shadow ring and want to have a better chance to get a good ring, you can make the transmog cost overflow and then transmog your ring.
If you don't want to change your build for overflow, you can get a torch (especially by bombing activated darkness) for this strat.
I learned this from Ocre307's run.
All of speed-wise/score-wise bomb/bomb charm/grenade/nuke/blast helm/pulse/fireball/throwing stars/rifle foodshop kill with/without SSS can be found in this video.
(Synchrony~) blast helm no longer detonates bombs instantly (thus you can normally pick up the gluttony charm).
This video also includes:
All of Mary speed-wise/score-wise bomb/bomb charm/grenade/nuke/pulse/fireball foodshop kill with/without SSS can be found in this video.
This video also includes:
Faster than normal bomb kill.
Unlike other characters, Diamond doesn't need to buy items before blast helm kill even in legacy.
If you dig right, you need to buy right item (heart container) beforehand (or give it up).
If you dig right, you need to dig 1 tile above beforehand, or dig it with big dig (or tank a bomb, which can be negated by blast helm).
Lunging, earth, Dorian kills can be found in this video:
(Legacy) If you have lunging with blast helm, you don't need to buy items before the kill.