1. Set up the tiles.

Add to f_info (and remember to increase limit in misc.text):

--Was 214, 252 was next smallest unused number for the tile index
N:252:magic circle
G:.:v
F:FLOOR | DONT_NOTICE_RUNNING | SUPPORT_LIGHT | CAN_RUN
D:0:There is an aura of power here.

2. Set up ability in ab_info

--Was 7, now 12, for same reason as above
N:7:Draw circle
D:You can make magic circles
D:Prereq: Magic@30, INT@17, Meta@10
--m code was 102, now 133
A:102:Draw magic circle
--Reduced to 21 (3.5 levels of skillpoints), was 30 (5 levels of skillpoints)
I:21
k:30:Magic
k:10:Meta
S:17:INT

3. Set up mkey.lua
--^mkeys.lua in Furyband (though I'm not sure of the utility of the name change, personally)

add_mkey
{
	--Was 105, now 133
        ["mkey"] 	= 133,
        ["fct"] 	= function()
	--Cost was 50, changed to 30. No particular reason other than personal bias
			if player.csp > 30 then
                                increase_mana(-30)
				cave_set_feat(player.py, player.px, 215) 
	                	energy_use = 100
                        else
                                msg_print("You need at least 30 mana.")
                        end

        end,
}

4. Make it actually work! Add to spells.lua...

-- These functions overwrite (hopefully) the functions in lib\core\s_aux.lua
-- Only a couple of lines are changed, however
function get_level_school(s, max, min)
	local lvl, sch, index, num, bonus
        local allow_spell_power = TRUE

	lvl = 0
        num = 0
        bonus = 0

        -- No max specified ? assume 50
        if not max then
                max = 50
        end
	if not min then
                min = 1
        end

	-- Do we pass dependancies?
        if __tmp_spells[s].depend then
                if __tmp_spells[s].depend() ~= TRUE then
                        return min, "n/a"
                end
        end

        for index, sch in __spell_school[s] do
                local r, s, p, ok = 0, 0, 0, 0

                -- Does it require we worship a specific god?
                if __schools[sch].god then
                        if __schools[sch].god ~= player.pgod then
                                if min then return min, "n/a"
                                else return 1, "n/a" end
                        end
                end

                -- Take the basic skill value
                r = s_info[(school(sch).skill) + 1].value

        	-- Are we under sorcery effect ?
                if __schools[sch].sorcery then
                        s = s_info[SKILL_SORCERY + 1].value
                end

                -- Are we affected by spell power ?
                -- All teh schools must allow it for it to work
                if not __schools[sch].spell_power then
                        allow_spell_power = nil
                end

                -- Are we under a god effect ?
                if __schools[sch].gods then
                        p = get_god_level(sch)
                        if not p then p = 0 end
                end
                
                -- Find the higher
                ok = r
                if ok < s then ok = s end
                if ok < p then ok = p end

                -- Do we need to add a special bonus ?
                if __schools[sch].bonus_level then
                	bonus = bonus + (__schools[sch].bonus_level() * (SKILL_STEP / 10))
                end

                -- All schools must be non zero to be able to use it
                if ok == 0 then return min, "n/a" end

                -- Apply it
                lvl = lvl + ok
                num = num + 1
	end

        -- Add the Spellpower skill as a bonus
        if allow_spell_power then
		-- double for magic circle
            -- CHANGE1!
		if cave(player.py, player.px).feat == 214 then
	        bonus = bonus + (get_skill_scale(SKILL_SPELL, 20) * (SKILL_STEP / 5))
		else
  	        bonus = bonus + (get_skill_scale(SKILL_SPELL, 20) * (SKILL_STEP / 10))
		end
		
        end

	-- Add bonus from objects
        bonus = bonus + (player.to_s * (SKILL_STEP / 10))

        -- / 10 because otherwise we can overflow a s32b and we can use a u32b because the value can be negative
        -- The loss of information should be negligible since 1 skill = 1000 internally
        lvl = (lvl / num) / 10
	lvl = lua_get_level(s, lvl, max, min, bonus)

        return lvl, nil
end


function cast_school_spell(s, s_ptr, no_cost)
	local use = FALSE

	-- No magic
	if (player.antimagic > 0) then
		msg_print("Your anti-magic field disrupts any magic attempts.")
		return
        end

	-- if it costs something then some condition must be met
	if not no_cost then
	 	-- Require lite
		if (check_affect(s, "blind")) and ((player.blind > 0) or (no_lite() == TRUE)) then
			msg_print("You cannot see!")
			return
		end

		-- Not when confused
                if (check_affect(s, "confusion")) and (player.confused > 0) then
			msg_print("You are too confused!")
			return
		end

		-- Enough mana
		if (get_mana(s) > get_power(s)) then
                        if (get_check("You do not have enough "..get_power_name(s)..", do you want to try anyway?") == FALSE) then return end
	        end
        
		-- Invoke the spell effect
	        if (magik(spell_chance(s)) == FALSE) then
			if (__spell_spell[s]() ~= nil) then
	        		use  = TRUE
			end
		else
                        local index, sch

			-- added because this is *extremely* important --pelpel
			if (flush_failure) then flush() end

                        msg_print("You failed to get the spell off!")
			for index, sch in __spell_school[s] do
	                        if __schools[sch].fail then
        	                        __schools[sch].fail(spell_chance(s))
                	        end
	                end
			use  = TRUE
		end
	else
        	__spell_spell[s]()
        end

	if use == TRUE then
	        -- Reduce mana
		adjust_power(s, -get_mana(s))

	        -- Take a turn
        	if is_magestaff() == TRUE then energy_use = 80
	        else energy_use = 100 end
	-- destroy magic circle
      -- CHANGE2
     if cave(player.py, player.px).feat == 214 then
		cave_set_feat(player.py, player.px, 1) 
	end
	end

	player.redraw = bor(player.redraw, PR_MANA)
	player.window = bor(player.window, PW_PLAYER)


end