Summon Multiple (3+) Unit Types

I'm trying to make a hero spell based off Raise Dead that at level one, summons one type of unit, at level 2 summons both the level 1 unit as well as an additional unit, at level 3 summons both prior units AND an additional unit type, etc. BUT Raise Dead only seems to allow two unit types.

Alternatively, I've been trying to use triggers to have it summon a random unit based on spell level (for example, level four could spawn any of the unit types up to that point, and can spawn four units at a time, but level 1 could only summon the first unit type and only one unit total), but keep running into a billion different conditions trying not to let the trigger spawn more than once or at least kill the old unit of the same type.

Can anyone point me in the right direction?

Well, I'd make the spell summon just one kind of unit, and use a trigger to detect the level of the raise ability on the unit that summons the raised unit, and then swap the raised unit for whatever unit is supposed to be raised at that level.

I think dark portal allows you to summon groups of different types of units.

Unfortunately, Dark Portal doesn't summon from corpses.

Like Panto said, your best bet is to trigger the spell.

Alternatively you could use dummy casters. Have raise dead summon the level 1 unit. Triggers detect the level that the spell is and creates dummy casters that cast modified water elementals.