IntegerMax takes two integer inputs and outputs the larger of the two into another variable.

Code
IF
CharacterLeveledUp(_Char)
AND
IntegerMax(5, 10, _output)
AND
_output < 6
THEN
PartyAddExperience(_output); //Never occurs because _output will equal 10


For the OP, this code should do what you're wanting (if GoalComplete doesn't work)
Code
IF
CharacterTurnStarted(CHARACTER_Ulfred_GateKeeper_Boss)
AND
CharacterGetHitpointsPercentage(CHARACTER_Ulfred_GateKeeper_Boss, _health)
AND
_health < 50
AND
NOT DB_UlfredTriggered(1)
THEN
CharacterTeleportToTrigger(CHARACTER_Ulfred_GateKeeper_BossAdd000,TRIGGER_Ulfred_GateKeeper_BossAddPoint000,"Add was Spawned");
CharacterTeleportToTrigger(CHARACTER_Ulfred_GateKeeper_BossAdd001,TRIGGER_Ulfred_GateKeeper_BossAddPoint001,"Add was Spawned");
CharacterTeleportToTrigger(CHARACTER_Ulfred_GateKeeper_BossAdd002,TRIGGER_Ulfred_GateKeeper_BossAddPoint002,"Add was Spawned");
CharacterTeleportToTrigger(CHARACTER_Ulfred_GateKeeper_BossAdd003,TRIGGER_Ulfred_GateKeeper_BossAddPoint003,"Add was Spawned");
DB_UlfredTriggered(1);