These command bestow a status effect on the invoking character. This command is
used a lot in the item scripts.

// This would poison them for 10 min
sc_start SC_Poison,600000,0;

Effect type is a number of effect, 'db/const.txt' lists the common (mostly
negative) status effect types as constants, starting with 'SC_'. You can also
use this to give someone an effect of a player-cast spell:

// This will bless someone as if with Bless 10:
sc_start 30,240000,10;

Extra argument's meaning differs depending on the effect type, for most effects
caused by a player skill the extra argument means the level of the skill that
would have been used to create that effect, for others it might have no meaning
whatsoever. You can actually bless someone with a 0 bless spell level this way,
which is fun, but weird.

The target ID number, if given, will cause the status effect to appear on a
specified character, instead of the one attached to the running script. This has
not been properly tested.

'sc_start2' is perfectly equivalent, but unlike 'sc_start', a status change
effect will only occur with a specified percentage chance. 10000 given as the
chance is equivalent to a 100% chance, 0 is a zero.

'sc_start4' is just like sc_start, however it takes four parameters for the
status change instead of one. What these values are depends on the status
change in question. For example, elemental armor defense takes the following
four values:
- val1 is the first element, val2 is the resistance to the element val1.
- val3 is the second element, val4 is the resistance to said element.
eg: sc_start4 SC_DefEle,60000,Ele_Fire,20,Ele_Water,-15;

'sc_end' will remove a specified status effect.

You can see the full list of status effects caused by skills in
'src/map/status.h' - they are currently not fully documented, but most of that
should be rather obvious.