Boost slots and Diamond slots add more levels to minis in your Leader’s army. Boost slots help you to use minis that you have not leveled up yet, and Diamond slots are needed to upgrade your minis to the highest possible level.
Boost Slot
Boost slot is a special army bonus slot in Warcraft Rumble that provides the mini in the slot with full XP levels (20). This enables you to play with unleveled minis like they would have already reached the XP cap. The slot has no effect on XP-capped minis.
Boost slots are earned by defeating the first wing in the normal Molten Core raid (Lucifron and Magmadar). With the current co-op rotation, you get one Boost slot every four weeks.
When you earn a Boost slot, you can use it on any Leader that you own, not just the one you used to defeat the bosses. If you leave the selection screen, you can come back to it later, but you cannot progress to wing 2 of Molten Core without choosing the Boost slot Leader.
Each Leader can only have one Boost slot, and it always buffs the bottom right slot of the Leader’s army board.
Diamond Slot
Diamond slot is an upgrade to the Gold army bonus slots, and adds +4 levels to the mini in the slot. It is currently the only way to reach level 11 in PvP: you need a max XP Legendary mini in a Diamond slot to reach level 31 in PvE, which translates into level 11 in PvP.
Diamond slot works well in combination with a Boost slot. Boost slot allows you to use a non-maxed Legendary mini at the highest level. You can also use a Rare mini in a Diamond Boost slot to reach level 28, enough for level 10 in PvP.
Diamond slots are purchased from Army Upgrades in the Army screen. You can freely choose which slots you upgrade. Each Diamond slot costs 200 Valor, and they are Leader-specific. Each Leader can have up to 7 Diamond slots at the cost of 1400 Valor, and you can upgrade individual slots as needed.
Valor is earned from Raids and Sieges as follows:
- Molten Core: 100 Valor from each boss - a full clear of both Normal and Heroic gives 1400 Valor
- Siege of Stormwind and Siege of Ironforge: 200 Valor from the first boss in Normal; 100 Valor from the first boss and 150 Valor from the second boss for Heroic clears after the first one - a full clear of both Normal and Heroic gives 450 Valor
There are 23 Leaders in the game, so upgrading every possible slot to Diamond costs 32,200 Valor. Because Raids and Sieges alternate every two weeks, you can earn up to 1850 Valor every four weeks. Fully upgrading everything will therefore take around 1 year and 5 months.
Spend Valor on good Leaders, but do not waste it.
Best Leaders to Upgrade with a Boost Slot
When you get your first Boost slot, you should not think too far. The Boost slot comes from the first wing of Molten Core and should be spent on a Leader that will best help you progress in Molten Core. There are several alternatives, and good ones can be Jaina (for Ragnaros, or pretty much any boss), Rend (for Geddon), and Emperor Thaurissan (for Ragnaros with Worgen).
Beyond that, Leaders that help you progress through the more difficult Molten Core bosses and Onyxia (Arthas, Drakkisath), as well as Leaders you want to use in PvP (depends on the modifiers and balance changes, but Arthas is strong right now) are the best targets for a Boost slot.
Overall, here is my take of the top-10 Leaders for a Boost slot:
- Jaina (strong against Ragnaros, very flexible)
- Arthas (the latest strong Leader, good in PvP and against Onyxia)
- General Drakkisath (strong in multiple Molten Core fights, viable against Onyxia, and sees some PvP play as well)
- Rend Blackhand (strong against Baron Geddon)
- Emperor Thaurissan (strong against Ragnaros, especially with a Boost slot Worgen)
- Malfurion (strong, flexible Leader)
- Sylvanas Windrunner (strong against Baron Geddon)
- Orgrim Doomhammer (strong, flexible Leader)
- Ysera (strong against Golemagg)
- Ragnaros (the best Leader against Baron Geddon)
Best Uses for Diamond Slots
The top use for Diamond slots is PvP because they are the only way to reach level 11 minis. However, they are strong in PvE progression content as well.
Combining a Diamond slot with a Boost slot can be especially powerful early on because it makes any Rare mini that matches the slot trait into a level 28 (PvP level 10) in that army.
Upgrading your PvP army in full can be strong, although it depends on whether you hit the level breakpoints (31 for 11, 28 for 10, 25 for 9) thanks to the upgrade.
Other than that, you want to upgrade the armies of Leaders you use for the hardest PvE content, such as Onyxia (some of the top Leaders to beat her include Arthas, Ragnaros, and Drakkisath).
You can also leave Valor unspent, waiting for a specific need so that you can immediately get a level when it matters. I generally spend Valor right when I need the levels.
