Thanks for the latest update; I had collected a few things on 0.51 which are listed below; recognise these might have been fixed already.
Looking forward to having a bash at the updated module. RE next thing to develop; - to be honest the thing I'd love to see is some animation with arrows, bolt spells and breaths - though this might not be easy to do. It'd be nice to see where stuff is coming from when you get blasted.
Thanks for the good work
Stay safe
Game functionality things:
If you go over your 100% burden limit, then you'll slow down (appropriately

If you consume or sell something to get you below that limit, you will remain at the penalised rate until you drop an additional item onto the floor - it's not updating the speed penalty check as far as I can see...
A voidgate destination was the princess - is this allowed?
Are empty bottles fillable?
Child spirits are friendly, but unless you can see them you can't move past them
If you recharge a staff, it seems at least on first go, to completely unidentify it (e.g. an identify staff (0 charges) becomes a cedar staff
In vaults aquatic creatures generated on land
Error reports
Fails to load when attempting to enter the heart of the world
on level change - I presume a fate would have triggered here...
error = "Game version: tome2-0.5.0\
Addons: gond_book-0.3.0, landmark-0.2.0, town_neutral-0.3.0\
\
Lua Error: /mod/class/interface/PlayerFates.lua:83: attempt to index global 'Map' (a nil value)\
At [C]:-1 __index\
At /mod/class/interface/PlayerFates.lua:83 ok_cb\
At /mod/spell-util.lua:1058 \
At [C]:-1 calc_circle\
At /mod/spell-util.lua:1066 grids_near\
At /mod/class/interface/PlayerFates.lua:89 apply\
At /mod/class/interface/PlayerFates.lua:224 checkFates\
At /mod/class/Game.lua:600 changeLevel\
At /mod/class/Game.lua:1162 \
At /engine/KeyBind.lua:243 "
seen = true
reported = false
Attempted to copy a spell to a stack of amulets of spell
error = "Game version: tome2-0.5.1\
Addons: gond_book-0.3.0, landmark-0.2.0, town_neutral-0.3.0\
\
Lua Error: /mod/class/Actor.lua
stack traceback:\
\9/data/talents/skill/magic.lua:61: in function </data/talents/skill/magic.lua:44>\
\9[C]: in function 'xpcall'\
\9/engine/interface/ActorTalents.lua:186: in function </engine/interface/ActorTalents.lua:173>\
At [C]:-1 \
At [C]:-1 error\
At /mod/class/Actor.lua:1779 unload\
At /engine/Game.lua:467 unregisterDialog\
At /mod/dialogs/UseTalents.lua:195 use\
At /mod/dialogs/UseTalents.lua:120 fct\
At /engine/ui/TreeList.lua:310 onUse\
At /engine/ui/TreeList.lua:209 fct\
At /engine/Mouse.lua:71 receiveMouse\
At /engine/Mouse.lua:111 delegate\
At /engine/ui/Dialog.lua:798 mouseEvent\
At /engine/ui/Dialog.lua:508 fct\
At /engine/Mouse.lua:71 "
seen = true
reported = false
Got a really good character to level 29:
Had a couple of issues where the character accidentally targetted itself with bolt spells and expired; - I did retrieve the characters as seemed a shame to lose the progress. It seems to happen perhaps because the user interface can't keep up with key-presses and then it accidentally targets the player; which will often be fatal. Not sure what you think about effectively all spell casters having immunity to their own spells? shame to die with a typo.
Anyway, the following error messages started coming up.
error = "Game version: tome2-0.5.1\
Addons: gond_book-0.3.0, landmark-0.2.0, town_neutral-0.3.0\
\
Lua Error: /engine/interface/ActorTalents.lua:351: /engine/interface/ActorTalents.lua:324: /engine/interface/ActorTalents.lua:190: /engine/interface/ActorTalents.lua:158: attempt to index upvalue 'force_target' (a nil value)\
stack traceback:\
\9/engine/interface/ActorTalents.lua:158: in function 'getTarget'\
\9/mod/spell-util.lua
\9/data/talents/spell/mana.lua:69: in function </data/talents/spell/mana.lua:68>\
\9[C]: in function 'xpcall'\
\9/engine/interface/ActorTalents.lua:186: in function </engine/interface/ActorTalents.lua:173>\
At [C]:-1 \
At [C]:-1 error\
At /engine/interface/ActorTalents.lua:351 useTalent\
At /mod/class/Player.lua:701 useTalent\
At /engine/interface/PlayerHotkeys.lua:179 \
At /engine/interface/PlayerHotkeys.lua:162 activateHotkey\
At /mod/class/Game.lua:1341 fct\
At /engine/interface/PlayerHotkeys.lua:326 \
At /engine/KeyBind.lua:231 "
seen = true
reported = false
error = "Game version: tome2-0.5.1\
Addons: gond_book-0.3.0, landmark-0.2.0, town_neutral-0.3.0\
\
Lua Error: /mod/spell-util.lua
At [C]:-1 \
At [C]:-1 error\
At /mod/spell-util.lua:2835 cast\
At /mod/dialogs/UseThaumaturgy.lua:183 use\
At /mod/dialogs/UseThaumaturgy.lua:97 fct\
At /engine/ui/TreeList.lua:310 onUse\
At /mod/dialogs/ui/TweakedTreeList.lua:177 fct\
At /engine/Mouse.lua:71 receiveMouse\
At /engine/Mouse.lua:111 delegate\
At /engine/ui/Dialog.lua:798 mouseEvent\
At /engine/ui/Dialog.lua:508 fct\
At /engine/Mouse.lua:71 "
seen = true
reported = false