fix(Core/XP): Reduce XP when ungrouped high-level player helps kill

[Nyeriah]

Changes Proposed:

This PR proposes changes to:

• Core (units, players, creatures, game systems).
• Scripts (bosses, spell scripts, creature scripts).
• Database (SAI, creatures, etc).

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Description

When an ungrouped player whose level makes the mob gray assists in killing a creature tagged by a lower-level player, the tagger now receives halved XP instead of the full amount. Currently the tagger receives full XP, which enables a power-leveling exploit where a high-level player leaves the group to grant full XP to a lower-level character.

Implementation:

• Tracks the highest player attacker level on each Creature during combat via _highestPlayerAttackerLevel, updated in LowerPlayerDamageReq() alongside existing damage tracking
• On creature death, KillRewarder::_RewardXP() checks whether the mob is gray for the highest attacker (using existing GetGrayLevel()) and if so, halves the XP using the same formula as the group gray-member penalty (xp / 2 + 1)
• The field resets on evade/respawn in ResetPlayerDamageReq()
• Only applies to the solo (non-group) reward path — group XP already handles level differences

Issues Addressed:

• Closes [Core] - Experience doesn't get properly reduced when a higher level player kills a lower level player's mob #24191

SOURCE:

The changes have been validated through:

• Live research (checked on live servers, e.g Classic WotLK, Retail, etc.)
• Sniffs (remember to share them with the open source community!)
• Video evidence, knowledge databases or other public sources (e.g forums, Wowhead, etc.)
• The changes promoted by this pull request come partially or entirely from another project (cherry-pick).

Source: https://wowpedia.fandom.com/wiki/Mob_experience#Solo_Experience_Modifiers

"The XP you receive depends on if that someone else will receive xp for killing that mob. If yes, you get full XP. If not, you get a tiny fraction."

Tests Performed:

This PR has been:

• Tested in-game by the author.
• Tested in-game by other community members/someone else other than the author/has been live on production servers.
• This pull request requires further testing and may have edge cases to be tested.

How to Test the Changes:

• This pull request can be tested by following the reproduction steps provided in the linked issue
• This pull request requires further testing. Provide steps to test your changes. If it requires any specific setup e.g multiple players please specify it as well.

1. Create two characters: one level 8, one level 80 (.level 7 and .level 79)
2. .cheat god for both, .tele rfc for both
3. Grouped test (baseline): Group both characters, kill a level 13 Earthborer with the level 80 → level 8 gets ~12 XP (existing behavior, unchanged)
4. Ungrouped test (fix): Leave group. Tag a level 13 Earthborer with the level 8, kill it with the level 80 → level 8 should now get ~128 XP instead of 255
5. Solo test (no regression): Kill a level 13 Earthborer solo with the level 8 → should still get 255 XP
6. Same-level helper test: Use a level 10 ungrouped helper instead of level 80 (mob is NOT gray for level 10) → level 8 should get full 255 XP

Known Issues and TODO List:

• The "tiny fraction" described by Wowpedia is implemented as the group gray-member formula (half XP). The exact Blizzlike fraction is not precisely documented — this may need tuning based on further research or sniff data.

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[Copilot]

Pull request overview

Adjusts solo XP rewards to mitigate a power-leveling exploit where an ungrouped high-level helper (for whom the mob is gray) enables a low-level tagger to receive full XP.

Changes:

• Track the highest player attacker level per Creature during combat.
• Apply a solo XP penalty on kill reward when the mob is gray for the highest-level attacker (halving XP via xp / 2 + 1).
• Reset the tracked highest attacker level on Creature damage requirement reset.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/server/game/Entities/Unit/Unit.cpp	Passes attacker player level into Creature::LowerPlayerDamageReq while dealing damage.
src/server/game/Entities/Player/KillRewarder.cpp	Applies solo XP reduction when the mob is gray for the highest-level attacker.
src/server/game/Entities/Creature/Creature.h	Extends damage tracking API and exposes highest attacker level getter.
src/server/game/Entities/Creature/Creature.cpp	Stores/initializes/resets _highestPlayerAttackerLevel and updates it during damage tracking.

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[Copilot]

xp = xp / 2 + 1 can incorrectly turn an already-zero XP reward into 1 (e.g., if earlier logic set xp = 0 due to no-XP conditions). Add a guard so the reduction only applies when xp > 0 (or restructure so the “+1” is only used when the base XP was positive), ensuring no-XP kills remain no-XP.

Suggested change

	if (creature->GetLevel() <= grayLevel)
	if (creature->GetLevel() <= grayLevel && xp > 0)

[Nyeriah]

This can't happen in practice. The solo path (else if) is mutually exclusive with the if (_group) branch, which is the only place xp gets zeroed. In the solo path, xp starts as _xp and nothing sets it to 0 before reaching this code.

Additionally, the caller already guards against this — _RewardXP is only invoked when _xp > 0 (line 214: if (_xp)), and _xp is a member that doesn't change during the reward flow.

[Nyeriah]

Tested but could use more testing

[TheSCREWEDSoftware]

Tested but could use more testing

The testing steps could even applied in world of having a level 60 helping farming mobs south of elywirn forest for full XP capped to your level ranged (prior to this, have not tested this and wont be able most likely during the weekend)

[Nyeriah]

Its enough to pull a mob and hit it with a higher level player, I think